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Hello everyone. Welcome to the first
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lesson about the principles of reinforce
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concrete design.
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First ting
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what is the definition of reinforced
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concrete.
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So of course concrete unahin natin no
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concrete is a mixture of sand, gravel,
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crush rock or other aggregate. So ang
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division nito is it could be a course
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aggregate or a fine aggregate. And they
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are held together with a into a rocklike
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mass.
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with the pace of binder. Now, iyung
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binder natin, it could be Portland
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cement or asphalt cement. So, we have
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Portland cement concrete and we also
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have asphalt cement concrete. Now, dito
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sa image, it's using cement. At pagland
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cement yung gamit natin, this is
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activated by water. So, magre-react
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iyung water doon sa cement para
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mag-harden siya.
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Sometimes also if you can look here we
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add what we call add mixtures to change
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yung certain characteristics ng concrete
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such as yung workability niya,
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durability or yung time of hardening.
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Now what is reinforced concrete?
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Reinforced concrete is a combination of
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concrete and steel wherein the steel
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reinforcement provides stencil strength
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locking in the concrete. Kasi iyung
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concrete natin no, ah concrete is
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actually very weak in tensil or tension
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stresses. That's why we provide
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additional support para doon sa tension
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forces natin. So ito for example we have
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a beam which is made up of plane
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concrete. So if you push it with the
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load no P
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iyung bottom nung beam will have tension
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forces. So magka-crack siya doon because
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concrete cannot actually handle a lot of
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tensil stresses. So magka-crack siya
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doon. So ang ginagawa natin, we
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reinforce it. We introduce a
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reinforcement steel do sa ilalim to
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handle those tension forces. So ito yung
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reinforce concrete.
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We have several advantages ng reinforced
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concrete. One of those advantages is
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that it has considerable compressive
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strength. So kung mahina man siya sa
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tension ah we have to know na we have to
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understand that iyung concrete is
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actually very strong in compression. So
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yung iyung concrete natin at saka iyung
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steel bars they complement each other
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kasi iyung concrete malakas sa
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compression iyung steel natin malakas sa
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ah tension. Okay. So, one of the
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advantages
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compared doon sa unit cause niya,
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maganda yung compressive strength ng
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rainforce concrete. Also, it has great
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resistance to the actions of fire and
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water. In fact, it's the best material
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available for situations where water is
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present. So ano bang ibang material na
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available? We have wood at saka
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structural steel, no? So, si wood in
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presence of water, nagkakaroonya ng
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molds. Nagra-rut siya. si steel of
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course kung kung mga water applications
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kakalawangin now reinforce concrete. Si
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concrete no ah acts as a protection of
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protective cover doon sa mga steel bar
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sa loob niya. Reinforce concrete
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structures are very rigid. When we say
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very rigid, ibig sabihin ah it's not
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swaying much, no? Hindi siya masyadong
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nagsu-sway lalo na versus lateral
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forces. That's why one of the best
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systems na ginagamit natin to counteract
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lateral forces is yung tinatawag na uh
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reinforce concrete sheer walls because
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those are very rigid walls and very good
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when there are lateral forces present.
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It is a low maintenance material. We do
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not need to repaint or to to protect it
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against rusting ' ba. Yun yung
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nangyayari kapag mga steel structures
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you have to maintain it against yung mga
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rust. Si concrete. If if you do it
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right, if you maganda yung pagkakaw
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natin, makinis yung yung mga sides niya,
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it won't have a high maintenance cost.
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As compared with other materials, it has
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a very long service life. Okay? And it
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is usually the only economical material
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available para sa mga putings, slabs,
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basements, and other applications kung
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saan the structure is very massive, no?
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If even you have a very massive volume
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of structures, automatic concrete iyung
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ginagamit natin. We don't do for example
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footings. We don't do a lot of steel
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footings no or wala atang ganon no meron
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siguro yung mga steel piles pero usually
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concrete talaga ang ginagamit. Now a
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special feature of concrete of course is
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the ability to be cast into different
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shapes. So simple slabs, beam columns.
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Pwede mo siyang i-shape as arches,
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shells, no? Yung mga shell structures,
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mga naka-curve na na mga shape. Kasi the
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shape of the reinforced concrete
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structure will be based
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na gagamitin natin. Tapos ah kumbaga
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liquid kasi siya nilalagay ' ba. And
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then we will uh wait for it to cure at
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mag-harden to take the shape of whatever
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is the form na ginamit natin. In most
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areas, concrete takes advantages of or
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advantage of inexpensive local material.
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So what are the local materials? You
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have sand, gravel, and of course the
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water used para mag-react doon sa
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Portland cement. So madali siyang kunin.
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You don't need to mine yung katutulad sa
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steel 'di ba? You have to mine yung
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steel orses to refine it para magkaroon
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ka ng steel structure. So usually yung
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mga steel steel natin sa Pilipinas we
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import them uh from other countries.
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Now, pagdating naman sa wood, we don't
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need to chop trees. 'Di ba in in dito sa
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atin kasi wala na tayong ano no, yung
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mga forest nakakalbo na so mahirap. So
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ito madaling iano i-source yung material
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ng concrete. Okay? And a lower grade of
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skilled labor is required for the
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erection compared with other material
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such as structural steel. So
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buhos-buhos, sainta-sinta and then
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that's it. Pag sa structural steel kasi
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ah lalo na yung mga talagang malalaking
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structure you have to have skilled labor
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para doun sa mga welding non. Hindi yun
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spot spot welding lang. Okay. So, mas
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madali siyang ah gawin ng mga labor
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natin.
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Now, of course, there are also
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disadvantages when using reinforced
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concrete. One of that is that concrete
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has very low tensil strength which
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requires the use of tensil reinforcing.
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Of course, uh this is a disadvantage and
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also somewhat an advantage kasi
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still actually uh
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compliments no iyung concrete natin. So
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you are still forced to use a steel
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material. Okay? Ah hindi lang purong
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concrete. Forms which are expensive are
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required to hold the concrete in place
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until it hardens efficiently. Ah ibig
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sabihin
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when when you do a concrete structure
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pag nilagay mo yung yung beam mo yung
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concrete beam mo hindi siya agad agad
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nagagamit you have to wait for it to
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attain a certain level of strength ba
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yung mga 7 14 days strength na alam
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natin no and bago mo mapatungan ng load
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yung structure natin okay so you have
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to to wait for it to cure.
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before the members gain sufficient
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strength to support themselves.
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Number it has low strength per unit of
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weight of concrete so it leads to heavy
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members. So concrete structures are
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heavier than structural steel
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members dahil massive yung mga volume
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nila, malalaki yung members. And this
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becomes a constraint no when you want to
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do long span structures.
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Uh yung concrete is heavy. It's large.
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It has large dead weight. No, this this
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should be weight.
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Yan weight
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and has great effect on the bending
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moments kasi nga concrete concrete
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structures are heavy no heavy members
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compared with structural steel. Now
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similarly low strength per unit of
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volume of concrete means members will be
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large relatively large and this is an
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important consideration for tall
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buildings and long span structures. So
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an example of this is when making great
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force concrete beams no uh if you want
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to span 6 meters
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typically a concrete beam would be half
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a meter deep. Okay. Half a meter deep
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and half of that would be yung
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structural steel. So ibig sabihin for to
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span 6 meters si concrete nasa 500 mm
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yyung depth. Pag steel 250 to 300 mm
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lang yung depth. So mas malalaki talaga
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yung concrete members versus sa steel.
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So that's one of the disadvantage.
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Number five, it has something to do with
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the the quality control. Properties of
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concrete vary widely because of the
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variations in proportioning and mixing.
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Furthermore, placing and curing of
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concrete is not as carefully controlled
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as is the production of other material
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such as structural steel and laminated
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wood. Now, dahil yung paggawa ng
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concrete is
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depende sa contractor kung paano nila
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pino-proportion, medyo mas may varation
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yung ano no mga properties nito. For
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example, you can specify sa structural
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design mo na 28 megapascal or 4,000 PSI
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yung strength. In actual, it won't be 28
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megapal. It won't be 4,000. It could be
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lower or higher. No, but we accept that.
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For example, 4,000 PSI ang specification
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and it comes out na naging 4,500, 4,700,
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4,200
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we will still accept that because 4,000
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yung minimum specs natin. But if if you
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look at it from the point of view of
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efficiencyo, parang yyung 4,700 masyado
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ng mataas kaysa sa 4,000
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but it's still good. Okay yun medyo mas
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malaki lang iyung variation nung nung
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concrete ah strength.
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Okay. Now, let's go sa concrete and
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steel. Ah in this in this part of our
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lesson, we will talk about the different
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properties of concrete and the different
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properties of steel.
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Unahin natin si concrete class. So
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concrete is made by mixing cement and
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water. This is true for hydraulic
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cements. Okay. We need to use water para
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mag-activate yung hydraulic cement.
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Okay. Use in binding the aggregates
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which are sun and gravel which are the
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fine and c aggregates.
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The water cement ratio greatly affects
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the strength of concrete.
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We want a lower water cement ratio. But
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unfortunately if if the
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water is less no kung onti lang yung
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tubig na ginamit mo, the concrete mix
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will not be workable. Mahirap siya
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i-form pero pag napasobra ka naman ng
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tubig humihina yung strength.
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Okay. Now we also have the curing of
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concrete. Curing is performed by
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submerging the specimen underwater. This
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is done to prevent moisture loss. Kasi
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rapid moisture loss leads to cracking
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and loss of strength of concrete
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specimen. So if you can remember sa
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ating materials testing class no sa
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construction materials and testing
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we built concrete specimens cylinders
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and nilulubog iyun sa tubig no we are
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curing the concrete. In actual you
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cannot do that ' ba sa mga bahay sa mga
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structure sa mga building. You you
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cannot cure the concrete building by
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submerging everything in water. So in
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actual ang ginagawa ah during the
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crewing process we we
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[Musika]
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wet the surface of of the forms no
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dinidiligan yung yung mga slabs yung mga
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pader.
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Wini-wisikan ka ng tubig iyan every now
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and then to make sure that there will be
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no moisture loss. And one of the things
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that not mentioned here is you know
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iyung one of the purposes of of
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submerging in water or iyung pagwipisik
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ng tubig sa site is that we are also
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controlling the temperature because
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iyung reaction nung cement doon sa water
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it is ah I think it's called exothermic
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no it it releases heat no meron tayong
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tinatawag na heat of hydration and if
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you if you do not control that release
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of heat it would
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it would accelerate the moisture loss
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okay and th
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iina yyung concrete specimen natin.
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Okay? So yun yung ginagawa no? Meron
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tayong process na tinatawag na curing of
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concrete.
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Now let's look at the stress rain
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relationship of concrete. So stress
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strain relationship relationship will
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tell us or or is one of the basic
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mechanical properties of materials. So
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ito iyung stress strain graph natin.
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Yung strain natin would be nasa baba and
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then yung stress sa taas. So first is
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pag tinesting mo yung concrete you will
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reach some kind of limit. We call it the
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proportional limit. This is the limit
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where the stress and strain are
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proportional. So we connect it with a
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straight line. Now
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after that we will reach what we call
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the elastic limit. This is the limit
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kung saan if you remove the load yung
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strain ko will go back to zero. No
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problem. Okay? Pero beyond that,
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magkakaroon ako ng tinatawag na
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permanent deformations. So in this
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region, we call this the elastic region.
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Ah meron tayong hooks law that the
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stress is directly proportional to
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strain up to the proportionality limit
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hanggang dito. So yung hooks law natin
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is yung yung proportional
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ah what do you call this? Yung
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proportionality factor natin is the
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modulus of elasticity. So yung stress is
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proportional sa strain and yung constant
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of proportionality
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E is what we call the modulus of
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elasticity. That's basically yung slope
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nitong graph na to. Okay? And then we
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will reach elastic limit. Ah hanggang
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diyan na lang yung limit na na
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after niyan meron ka ng permanent
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deformations.
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And then we will reach the ultimate
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compressive strength. Ito iyung F prime
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CO. The ultimate compressive strength.
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And then of course dito after nitong
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elastic limit meron na tayong nonlinear
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elastic region. And then we have the
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brake point. The braking or the rupture
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point the failure occurs. The concrete
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cracks in tension. So ito yung rupture
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point natin. Okay. Usually yung yung
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maximum strain na to we take it
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in European countries that would be
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0.0035
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3. Okay. 0.0035 sa atin 0.003.
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Okay.
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Now,
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meron tayong design codes. Of course, we
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have the national structural code of the
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Philippines. They provide detailed
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technical standards that are used to
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establish requirements nung actual
00:17:59
structural design. Nandiyan din
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naka-specify 0.003 003 as the maximum
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strain ng concrete. Ah it should be
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realized however that codes only provide
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guide for design. Okay. Remember yung
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ultimate responsibility will always lie
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with the structural engineer who is also
00:18:22
the engineer on record who signed the
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calculations and the plans. Nasa nasa
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kanila pa rin itong code na to. minimum
00:18:32
design standards. You can actually go
00:18:34
beyond the code or you can go below
00:18:38
provided that ah you have the
00:18:41
calculations to support yung yung design
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choices mo
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for the elastic modulus of concrete yung
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e subsecural
00:18:56
code about this value of subc. So from
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our national structural code 2015 ah we
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have two categories for normal weight
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concrete which is normal weight concrete
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which has a weight of 2,300 kg per cubic
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meter. So this is the density.
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We can assume that the modulus of
00:19:20
elasticity is 4,700
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lambda s root of f prime c and this a
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subc is in megapascals.
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For other weights naman where WC is not
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2,300
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we have this equation we have the the
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mass density rais to 1.5
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0.043 043 lambda s ro f prim c again
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this values would be in megapascals.
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Yung lambda natin it's a factor
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considered for the type of concrete.
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Usually it's one for normal weight and
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75 naman para sa mga lightweight
00:19:59
concrete. Light weight is anything below
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2,300 kg per cubic m.
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Now for the ultimate compressive
00:20:09
strength of concrete, ito yung this is
00:20:11
the top portion nung ating stress strain
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curve. It is the maximum value na
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pwedeng ma-attain without
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uh breaking the concrete. So for a
00:20:24
commercially available concrete, this
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are in multiples of uh 7 megapcal
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starting from 17. This would be the
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accepted lowest value. And then we have
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21, 28, 34 and so on. So + 7 ng + 7 to.
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21 megcal corresponds to 3KSI or 3,000
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PSI and then dagdag ka ng 1,000
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or 1KSI or 7 megascal. So we have 28 34
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and so on. So ang conversion factor nito
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actually is 1KSI is 6.896 896 megapcal.
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So sa iba ginagawa na lang na 7 megapal.
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So 1 ksi is 7 megapal. But anyway, here
00:21:09
is the more accurate conversion factor.
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Now for the design and analysis of
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reinforced concrete uh we have first is
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what we call the working stress design
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method.
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Uh the assumption is that the concrete
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is linear uh elastic ang kanyang
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behavior. And ibig sabihin
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ah the consideration is hanggang doon
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lang sa proportional limit. So pag
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sinabing linear elastic doon lang tayo
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sa proportional limit d sa graph kanina.
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For ultimate strength design method
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naman the behavior of concrete is
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nonlinear. So lalampas tayo doon sa
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proportional limit.
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Okay, this is considered hanggang doon
00:21:56
sa ultimate strength. So this two
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methods are the design methods used sa
00:22:03
pagde-design ng concrete. Actually USD
00:22:05
has is the main method of design sa
00:22:08
reinforce concrete. USD ultimate strent
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design because it it just makes sense no
00:22:13
na na you would be considering yung
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ultimate strength at hindi mo i-limit
00:22:18
yyung sarili mo doon sa proportionality
00:22:20
limit. But still working stress design
00:22:23
is still used today uh in particular sa
00:22:28
mga ano structures that retain water or
00:22:31
has
00:22:33
water
00:22:35
feature na na kailangan mong i-limit
00:22:38
yung mga cracking para hindi mag
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magkaroon ng mga leak no mga water tank
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na concrete. Most of them are still
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designed are still designed using
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working stress design. Okay.
00:22:54
Now other properties of concrete we have
00:22:57
shrinkage and crip. Shrinkage this is
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the contracting of harden concrete due
00:23:02
to loss of water and moisture. Ah
00:23:05
shrinkage temperature bars are used. So
00:23:09
yung mga rebar natin is not just for the
00:23:13
tension stresses but also to prevent
00:23:17
itong excessive cracking because of the
00:23:19
contraction of concrete. Okay? Shrink
00:23:23
cage. So that's that's why yung
00:23:25
temperature bar shrinkage temperature
00:23:27
bars we also call it or I like to refer
00:23:30
to it as shrinkage and temperature
00:23:34
control bars. So controlling this
00:23:37
phenomena.
00:23:38
We also have creep. This is the
00:23:40
additional deformation because of the
00:23:42
load applied for a very long time. So
00:23:45
when when you have a very long
00:23:49
time of load application, creep happens,
00:23:53
nagre-rearrange yyung ano yung mga
00:23:55
particles ng concrete. Nagkakaroon ng
00:23:57
permanent deformation. So this is an
00:23:59
example of a bridge that has experienced
00:24:03
crif deflection. So makikita niyo
00:24:05
pagdating dito hindi napantay yung
00:24:06
bridge. Nag-lower down na siya dito. And
00:24:10
it's it's not because mahina yung
00:24:12
konkreto.
00:24:14
It's not because uh na-overload. If you
00:24:18
look at it, there's no truck sa taas.
00:24:22
But it's it's quite something like the
00:24:25
secondary consolidation sa soil no na
00:24:29
due time overtime concrete wood would
00:24:32
have this permanent deformations.
00:24:38
Now for the steel we have longitudinal
00:24:40
bars. Ito yung tinatawag natin na rebar.
00:24:44
Uh noon they use plane bars which has
00:24:48
smooth surface but it failed kasi hindi
00:24:52
siya kumakapit sa konkreto. So after
00:24:55
that they introduce yung deformations
00:24:59
doon sa bar. Ah before we have this kind
00:25:02
of bar ito yyung may mga rides and logs
00:25:05
no? Before we had that we have plain bar
00:25:08
na square tapos tini-twist. Naka-twist
00:25:10
siya. So para siyang parang ano ah meron
00:25:14
siyang grooves dahil doun sa pagtu-twist
00:25:16
nung rectangular bars no. Para siyang
00:25:20
screw. Okay? But they found out na hindi
00:25:23
rin siya ganon ka-effective. So
00:25:24
naimbento itong deform bars which has
00:25:27
this
00:25:28
rinches at saka lugs na tinatawag. Okay,
00:25:32
ito yung mga ridge. Okay, itong itong
00:25:35
straight sa side, ito yung lugs.
00:25:38
Okay. Now, we also have prestress steel
00:25:41
which which would not be part of the
00:25:43
course, but this are also reinforcement
00:25:47
bars. But instead of solid reinforcement
00:25:50
bars na isang buo, these are made up of
00:25:54
high tension cable wires bundled
00:25:56
together. Yan, ganyan.
00:25:59
And then of course sa steel we have yung
00:26:02
structural steel shapes natin na
00:26:04
iba-ibang shape.
00:26:07
Note that reinforcing steel bars are
00:26:10
place where concrete is weak in tension.
00:26:13
So we have to know kung saan yung mga
00:26:17
tension stresses sa concrete at kung
00:26:19
saan malalaki 'yung tension stresses.
00:26:22
Doon natin pinupwesto yung yung ating
00:26:24
mga reinforcement bars kasi siya yung
00:26:27
magke-carry nung tension o tensil
00:26:29
stresses na yon.
00:26:33
So longitudinal bars, yung mga bars,
00:26:35
reinforcement bars comes in different
00:26:37
sizes. Actually hindi lang to
00:26:39
longitudinal basta reinforcement bar sa
00:26:41
reinforcement sa reinforce concrete
00:26:43
design. Ito yung mga usual na sizes. We
00:26:47
have the nominal diameters 10, 12, 16
00:26:51
hanggang 36 mm meron yan. And then yung
00:26:54
mga length available usually 6 meters
00:26:57
yung meron ah depende sa contractor kung
00:27:00
ano yung pipiliin nila dito na na length
00:27:02
no kung ano yung mas advantageous sa sa
00:27:05
kanila or sa inyo kapag kayo naging
00:27:07
contractor. Ah minsan may nakita na ako
00:27:10
gumamit ng 12 para wala ng putol no wala
00:27:13
ng lapping hanggang second floor kasi
00:27:16
two story lang naman kasya yun 12 sa
00:27:18
kanya. So you you could actually order
00:27:20
this. Okay. Uh this is also one of the
00:27:23
reasons no itong mga nominal length na
00:27:26
iba-iba. It's one of the reasons kung
00:27:28
bakit ah actually nasa construction side
00:27:32
yung ano cutting list. Okay? Kasi
00:27:35
magagawa mo yung cutting list. One of
00:27:38
what one of the things na kailangan mo
00:27:41
sa cutting list is gaano kahaba yung
00:27:43
oorderin mong bakal alam mo kung ilang
00:27:48
beses kang magpuputol nung bakal. Okay.
00:27:51
Now, we also have specified yield points
00:27:54
ayon sa mga different standards. We have
00:27:57
ASM.
00:27:59
Uh this is the I think this is American
00:28:02
Society for testing materials.
00:28:05
And then we have PNS. PNS is the
00:28:07
Philippine National Standard which we
00:28:11
follow
00:28:13
no sa NSCP. So for grade 33, ito yung
00:28:17
ito yung dati ang tawag dito structural
00:28:20
grade ah yung grade 33 and then we have
00:28:25
ah grade 40 and then grade 60. So
00:28:29
structural grade dati to tapos 40 yung
00:28:33
ano yung
00:28:35
ah high grade pero iba na ngayon. Wala
00:28:37
na on'tg ano hindi na dapat tayo gagamit
00:28:40
nung 33 ngayon no. Ang ginagamit na
00:28:43
natin, ang ina-accept na itong dalawa 40
00:28:46
at saka 60. So yung 40, grade 40 o 40
00:28:51
KSI pag kinonvert mo yan, that would be
00:28:54
275 megapc. yung 60 that would be 415
00:28:57
megcals. So from the previous iterations
00:29:01
ng NSCP, ito yung ito yyung ginagamit na
00:29:05
megapascals. But I guess they opted to
00:29:08
use ano ah two two significant figures
00:29:13
lang sa latest iteration ng code. So
00:29:15
dahil two significant figures lang
00:29:17
naging 280 saka 420 siya. Okay. So 280
00:29:22
saka 420 megapcals.
00:29:25
Now, paano ia-identify 'to? Ah doon pag
00:29:29
umorder ka ng bakal meron yang mga
00:29:31
kulay-kulay doon sa dulo. Pine-paint
00:29:34
nila. Okay? Usually yung yellow that
00:29:36
would be 280. Yung green yun yung 420.
00:29:40
Tapos white naman yung grade 33. Ah
00:29:43
'yung red ito ay makikita mo doun sa
00:29:46
kabila no? Sa kabila ah minsan 'yan
00:29:49
'yung sinasabi nila na weldable versus
00:29:51
nonweldable na rebars. But anyway ah
00:29:55
nag-iiba 'to depende doon sa
00:29:57
pag-o-orderan mo. Depende sa supplier.
00:30:00
Hindi hindi siya actually standard sa
00:30:02
atin. So you have to ask your supplier
00:30:05
baka may iba silang color coding na
00:30:07
ginagamit. Okay. And aside from that,
00:30:10
meron din yang mga naka-etch doon sa
00:30:12
side nung bakal para malaman mo kung ano
00:30:15
yung grade nung bakal.
00:30:18
Okay.
00:30:21
Now, para naman sa steel. So kanina we
00:30:23
we talk about the different properties
00:30:26
of ah iyung concrete no? Yung stress
00:30:29
strain relationship ng concrete. Now
00:30:32
tingnan naman natin yung steel. So sa
00:30:34
steel ganun din no? We have the
00:30:37
proportionality limit which is yung
00:30:39
stress natin proportional doon sa
00:30:41
strain. Next is yung elastic limit kung
00:30:45
saan beyond this magiging permanent na
00:30:48
yung deformations. And by the way yyung
00:30:50
elastic modulus ng steel given to sa
00:30:53
atin we consider it to be 200,000
00:30:57
megapascals. So this is a actually a
00:30:59
requirement for the steel meals to
00:31:02
produce steel na pag ginawa iyung steel
00:31:04
kailangan ito iyung module doun sa
00:31:05
elasticity niya 200,000 megapcals.
00:31:09
Now after that we have what we call the
00:31:12
yield point. Si yield point this is the
00:31:15
point at which kahit mag-apply ka
00:31:17
dagdagan or kahit hindi ka mag-apply ng
00:31:20
maraming stress. So magpa-flat line siya
00:31:23
no'. Hindi ka nag-apply ng maraming
00:31:25
stress pero yung strain ko nadadagdagan.
00:31:29
Point in which constant stress is
00:31:31
applied but strain is continuously
00:31:33
increasing. This is what we call the
00:31:35
yield point. And then after that we have
00:31:39
the ultimate strength and the break
00:31:41
point. Okay? Ang break point is
00:31:44
mapipingal siya. The failure occurs.
00:31:48
So ito ultimate 10 strength. Now, one
00:31:51
difference between this stress strain
00:31:53
relationship between concrete and steel
00:31:55
is that uh yung sa concrete that is in
00:31:59
terms of compression no compressive
00:32:01
load. Itong sa steel kapag tinesting to
00:32:04
this is in terms of ah tension. Okay?
00:32:08
Binabatak yung steel hanggang maputol.
00:32:14
So ito yung mga points of importance
00:32:17
kapag magte-testing tayo ng steel. These
00:32:20
are the
00:32:22
universal testing machine na ginagamit.
00:32:24
And as you can see here, ito yung
00:32:26
nangyayari no kapag hinihila niya yung
00:32:30
bakal, nandito yung sample. Hinihila
00:32:32
niya and then as you can see ah liliit
00:32:35
yung diameter hanggang maputol. Okay?
00:32:39
Mapuputol siya. 'Yan 'yung tinatawag na
00:32:41
necking. So ito 'yun necking
00:32:44
beyond point C beyond the ultimate
00:32:47
ultimate point magkakaroon na ng necking
00:32:49
hanggang maputol yung bakal.
00:32:56
Now let us discuss some structural
00:32:59
elements. Structural elements on
00:33:01
buildings where we usually use reinforce
00:33:06
concrete.
00:33:09
A structure refers to a system of
00:33:11
connected parts to support a load.
00:33:14
Important examples would be buildings,
00:33:16
bridges, and towers. So 'yun yung mga
00:33:19
basic categories ng infrastructure na
00:33:21
ginagamit natin bilang mga civil
00:33:24
engineer or mga kino-construct natin. Ah
00:33:27
when designing a structure it should be
00:33:30
safe. Merong aesthetics. Ah it's it's
00:33:34
the main concern of the architecture
00:33:37
profession. And then we have service
00:33:39
ability. yung service ability sa atin uh
00:33:44
it has something to do with the feelings
00:33:47
of the people using the infrastructure.
00:33:51
It could be that the building is safe
00:33:54
pero medyo maalog no ma-vibrate. I know
00:33:56
you have experienced that sa mga I think
00:34:00
yung sa mga malls minsan ganun no? Pag
00:34:02
maraming tao minsan mararamdaman mo
00:34:05
naglalakad 'yung mga tao and
00:34:07
nagv-vibrate 'yung sahig. That's an
00:34:09
issue yung mga ganong vibration that's
00:34:11
an issue of serviceability.
00:34:13
Okay. Now,
00:34:16
issues of service will be yung cracking,
00:34:18
no? Uh, why is it an issue? Kasi if if
00:34:23
your reinforced concrete has many
00:34:25
cracks, moisture could penetrate and
00:34:28
erode the steel bars. And iyung agag
00:34:32
nagco-coro-road kasi iyung steel bars,
00:34:34
ang nangyayari doon na dadagdagan iyung
00:34:38
volume nung steel bars kasi nagkakaroon
00:34:41
ng ano eh nagba-bind iyung oxygen sa
00:34:43
kanya so madadagdagan yung volume niya
00:34:46
and it would lead to more cracking kasi
00:34:49
lumalaki yun eh. Lumalaki yung bakal sa
00:34:51
loob pag kinakalawang. Okay? Ba't
00:34:54
lumalaki? Nadadagdagan ng kalawang. At
00:34:57
pag nadagdagan siya ng kalawang,
00:34:58
ipu-push niya yung concrete lalong
00:35:00
magka-crack. So it's it's a it's an
00:35:05
issue for us. But one of the main or
00:35:09
yung pinaka-main talaga natin dito itong
00:35:12
safety.
00:35:16
Okay? Ito yung safety. Bale ng hindi
00:35:18
aesthetics no? Bale ng walang finishes,
00:35:20
walang pintura. As long as our structure
00:35:24
is safe against what? Against iyung
00:35:28
iyung environmental
00:35:31
constraints natin is yung mga load no?
00:35:33
Yung load usually earthquake 'di ba?
00:35:36
Wind
00:35:38
yung dead load at saka live load.
00:35:42
So often this requires several studies
00:35:45
of different solutions before final
00:35:47
judgement can be made uh as to which
00:35:51
structural form is most appropriate.
00:35:54
Uh the design process is both creative
00:35:57
and technical and requires fundamental
00:35:59
knowledge of material properties which
00:36:01
is pag-aaral. Ito yung pinag-uusapan
00:36:03
natin. And the laws of mechanics which
00:36:06
govern material response.
00:36:09
Ah
00:36:11
yung pagde-design is you have to do a
00:36:14
preliminary design muna and then you
00:36:17
analyze it after that preliminary design
00:36:21
before you come up with the final
00:36:23
design. So ayan.
00:36:29
Now, one of the most basic structural
00:36:32
elements are the beams and gearders. So,
00:36:34
beams are usually straight uh horizontal
00:36:37
members to carry the vertical loads. Uh
00:36:41
quite often they are classified
00:36:43
according to the way they are supported
00:36:46
as indicated in this figure. Could be
00:36:49
cantiliver. We have the overhanging
00:36:52
beams. Ito yung overhanging beams. Ah we
00:36:56
have the discontinuous
00:36:59
beam. Ito yun. Wala siyang continuity.
00:37:03
Ah sorry that is continuous pala. Okay
00:37:07
continuous beam. Sabihin direiretso
00:37:09
siya. Simply supported. Canty labor
00:37:13
simply supported. Or we also call this
00:37:15
the prop beam.
00:37:21
Okay. And then we have the fixed ended
00:37:23
beams. Now beams are primarily designed
00:37:26
to resist bending moment. However, if
00:37:29
they are short, kapag short and carry
00:37:32
large loads, meron tayong sheer na
00:37:36
maggo-govern doon sa design. Magiging
00:37:39
sheer governed design pag maikli. Pero
00:37:42
usually beams kasi mahahaba yun. So
00:37:46
bending moment.
00:37:50
Now to continue uh for bending and
00:37:53
deflections if the structure deformation
00:37:56
disappear and the structure gains its
00:37:58
original shape when the actions are or
00:38:02
the actions causing this deformations
00:38:04
are removed the deformation are termed
00:38:07
as elastic deformation. Kapag naman
00:38:10
permanent yung deformation, that is
00:38:11
kahit tanggalin mo yung load hindi siya
00:38:13
bumabalik sa dati niyang appearance no
00:38:16
sa original niyang shape. Then that is
00:38:19
in elastic or plastic deformation.
00:38:22
Now pagdating sa beams, usually we have
00:38:25
positive moment makes the beam smile
00:38:30
and then negative moment makes the beam
00:38:32
frown. So ganito 'yung usual na
00:38:37
sign convention natin.
00:38:42
So here are examples of reinforce
00:38:44
concrete beams and gearders. So as you
00:38:46
can see uh these are the
00:38:50
gearders.
00:38:52
Okay? I think this are tie beams
00:38:55
kung kung nasa baba sila nung structure.
00:38:57
So I'm not sure. Ah okay. Nasa ano sila,
00:39:00
elevated sila. Ito na yung pangalawang
00:39:03
floor. Okay. Now, this are the
00:39:06
reinforcement cage. We have the
00:39:08
longitudinal bars. And then we have the
00:39:13
sterups na tinatawag doon sa beam. yung
00:39:15
paikot yun yung sterups. We also have
00:39:18
the term what we call effective depth.
00:39:20
That is from the extreme
00:39:24
compression hanggang doon sa centroid
00:39:27
nung steel bars. Hindi siya hanggang
00:39:28
doon sa baba no? Hanggang dito lang sa
00:39:31
mga steel bars. That is the effective
00:39:33
dep.
00:39:34
Okay.
00:39:38
So typically ito yung mga beam designs.
00:39:41
Ah meron kang longitudinal bars and then
00:39:45
merong mga cuts no ah L/ 20, L/5
00:39:52
mga ganyan, L/3
00:39:54
depending on the on the detailing na
00:39:57
ginagamit. I've seen L / 4 and L /3 most
00:40:02
of the time. Okay? Diyan siya
00:40:04
nagka-cutof at saka nagi-splice. Ganyan
00:40:07
ini-specify. So ito yung bakal.
00:40:10
So kung i-splice mo siya
00:40:13
dito yung mga splice points, no? Meron
00:40:15
meron ding computation kung gaano kahaba
00:40:18
dapat yan.
00:40:19
Okay. So this are typical details. And
00:40:22
then of course yung steerups natin hindi
00:40:25
na pinapakita pero yung sterups yun yung
00:40:29
yung mga paganito na.
00:40:32
Okay.
00:40:36
So we have flexure cracks. Usually this
00:40:39
is for the slabs and beams.
00:40:42
Okay. Flexure cracks originate from the
00:40:46
maximum moment region. And nangyayari to
00:40:50
when we have in adecate flexal capacity.
00:40:54
Kulang yung ano yung moment capacity. So
00:40:56
nagkakaroon ng cracking na vertical.
00:40:59
Okay, vertical cracking. So sao 'yan sa
00:41:03
taas banda
00:41:06
sa mid span dito sa gitna.
00:41:09
We also have sheer cracks. Originates
00:41:12
near supports because you have inadecate
00:41:15
sheer capacity. Ibig sabihin kulang yung
00:41:17
ano either kulang yung size nung
00:41:19
concrete or kulang yung steerups dito sa
00:41:23
mga portion na 'to. So ayan yung mga
00:41:25
diagonal cracking dito sa support. Yan
00:41:30
ganyan.
00:41:34
Now para naman sa mga columns, columns
00:41:36
are also structural elements na
00:41:40
ginagamit yung reinforced concrete. So
00:41:42
this are members that are vertical.
00:41:46
resist compressive loads. We call that
00:41:49
columns. So makikita mo dito meron akong
00:41:51
column. Ayan column. And they are
00:41:54
carrying multiple levels. Ito yung
00:41:57
ground floor slab. We have yung slab
00:41:59
one, slab two. We have kung minsan yung
00:42:02
may roof deck ' ba lahat yan ah
00:42:06
naka-connect yan sa mga beams. And yung
00:42:08
mga beams na yon naka-connect doun sa
00:42:10
column. to
00:42:13
to transfer all those loads papunta doon
00:42:16
sa foundation. So the columns are the
00:42:19
vertical elements resisting yung mga
00:42:21
downward forces.
00:42:25
So ties naman no kung sa beams meron
00:42:28
tayong steerups, sa columns meron tayong
00:42:30
ties. This are confinement to prevent
00:42:33
buckling. Buckling ng ano nung nung mga
00:42:37
actually this is not buckling nung nung
00:42:40
column but rather backling nung mga
00:42:42
bakal sa loob nung column. Kasi one of
00:42:45
the failure niyan ' ba kungwari ito yung
00:42:47
column natin.
00:42:50
Ah teka
00:42:52
let's say ito yung column.
00:42:57
So may mga bakal yan sa loob. One of the
00:42:59
failure kasi is kung kung yung ties mo
00:43:02
is masyadong malayo sa isa't isa, what
00:43:06
happens is that pwede ong magbackle
00:43:09
pagon palabas yung bakal no? Nagkakaroon
00:43:13
siya ng backlink palabas lalo na kapag
00:43:17
yung load natin is very very large, very
00:43:20
heavy. So mag-backle siya palabas ganyan
00:43:24
kapag inadicate itong ties. Ito yung
00:43:27
ties.
00:43:29
Yan t.
00:43:37
So ito yung backling effect. Ito naman
00:43:39
itong backling effect na to. This is due
00:43:43
to moment and instability. Ito yung
00:43:45
buong column yung pwedeng mag-backle
00:43:47
lalo na kapag mahaba masyado yung yung
00:43:50
length nung column. So again yung ties
00:43:53
usually used for confinement to prevent
00:43:55
backling nung longitudinal bars but
00:44:00
still yung colum mo as a hole could
00:44:03
buckle. So that that's one of the
00:44:05
failure na pwedeng mangyari sa columns.
00:44:08
So again, I'm just discussing some basic
00:44:11
ano 'no uh basic features no' features
00:44:16
ba o bugs? Features ng mga structural
00:44:20
elements natin na ginagamitan ng
00:44:22
reinforce concrete.
00:44:25
So of course meron tayong slab. slab or
00:44:27
the flat horizontal panels that support
00:44:30
the floor. Uh it is usually supported in
00:44:33
beams and gearers or directly by
00:44:36
columns. Pwedeng walang beam and gurner
00:44:38
no pwedeng columns. They carry iyung
00:44:41
gravity loads and transfer them to the
00:44:44
vertical components, columns or walls
00:44:47
and also act as horizontal diaphrams.
00:44:50
Ibig sabihin kapag may mga lateral loads
00:44:53
lalo na iyung mga earthquake load. Si
00:44:55
slab din 'yung nagta-transfer nung mga
00:44:57
inertial forces papunta doon sa ating uh
00:45:02
elements na nagre-resist nung nung
00:45:05
earthquake by transferring lateral load
00:45:08
to vertical components. Okay? We have
00:45:11
several types of slabs pero meron tayong
00:45:14
one way and two way floor systems and
00:45:17
and there are other types of slabs pero
00:45:19
most common itong dalawa sa reinforce
00:45:22
concrete design.
00:45:25
For the oneway floor system, this are
00:45:27
slab that is supported only on two
00:45:32
slides. No, you you could assum assume
00:45:35
na supported lang siya doon sa longer
00:45:38
side. Ito ay kapag yyung shorter span
00:45:41
over the longer span is less than5, the
00:45:45
one way slab bends in only one
00:45:47
direction. Nagbe-bend siya along the
00:45:49
shorter span at 'yung support niya
00:45:51
nandito sa longer span. Ito yung L.
00:45:55
Tapos yung bending niya no, nagbe-bend
00:45:58
siya doon sa shorter span. And because
00:46:01
of that, ah yung flexural design would
00:46:05
be yung paganito no along the short
00:46:08
direction yung flexoral design. 'Yung sa
00:46:10
longer direction, ung sa L direction,
00:46:12
hindi siya flexure design but rather, as
00:46:15
you can see here,
00:46:18
we have distribution rebar. Ito yung
00:46:22
pahaba. It's not flexure but
00:46:26
distribution rebar para lang
00:46:27
ma-distribute iyung load. and
00:46:31
also
00:46:33
do sa temperature control and cracking.
00:46:37
Okay? So ito lang sa short direction.
00:46:39
Ito lang yung dine-design natin for the
00:46:41
moments kapag one way floor system.
00:46:44
Again, one way floor system nagbe-bend
00:46:46
sa short direction, short direction ng
00:46:48
bending. Ganito. Supported siya. Assumed
00:46:51
to be supported only in the long
00:46:53
direction. Hindi na nagma-matter kung
00:46:55
may beam talaga dito or doon sa kabila.
00:46:58
Okay. As long as ito yung yung ratio
00:47:02
nung shorter span and longer span, ang
00:47:04
assumption natin one way. Again,
00:47:07
this is an idealistic assumption, no?
00:47:11
Ah, lalo na kung may began naman dito,
00:47:14
of course, yung beam na yon would would
00:47:16
support some part some portion of the of
00:47:18
the slab, but we ignore it and we just
00:47:21
assume na dito siya sa mas mahabang
00:47:24
site.
00:47:27
For the two way floor system naman,
00:47:29
kapag iyung S / Ler than 5, the load is
00:47:33
assumed to be delivered to the
00:47:35
supporting beams and gearders in two
00:47:37
directions. Kaya two way. Two directions
00:47:39
ibig sabihin yyung along S at saka yyung
00:47:42
along the length na mga beams. Okay?
00:47:45
This is referred to as a twoway slab
00:47:47
system. So ito yung example yung bending
00:47:51
niya is in both directions lalo na kapag
00:47:55
supported ng apat na beam.
00:47:58
So that ends the presentation
00:48:03
if you have any question please
00:48:06
comment or tell me you could comment
00:48:11
below
00:48:13
thank No.
