The floor framing consists of one-way concrete joists spaced at 3'-0" centers. The concrete joists have a clear span of

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The Floor Framing Consists Of One Way Concrete Joists Spaced At 3 0 Centers The Concrete Joists Have A Clear Span Of 1 (100.27 KiB) Viewed 33 times

The Floor Framing Consists Of One Way Concrete Joists Spaced At 3 0 Centers The Concrete Joists Have A Clear Span Of 2 (186.73 KiB) Viewed 33 times

a) Assume 3,000 psi concrete and Grade 60 steel. Find thedesign flexural strength of the concrete joists for positive andnegative bending (Hint: In regions of negative bending, thedistance d to the reinforcing steel will be from the bottom of thejoist to the steel located in the slab. Recall that allconcrete below the neutral axis is assumed to be cracked. Thejoist taper and steel located at the bottom of the web may beignored for the flexural analysis in negative bending regions.)
b) In addition to the self-weight of the floor framingsystem, there is a superimposed dead load of 15 psf for mechanicalducts, electrical wiring, and ceiling loads. Determine themaximum uniform service live load that can be supported by thefloor joists.
The floor framing consists of one-way concrete joists spaced at 3'-0" centers. The concrete joists have a clear span of 35'-0" between concrete girders. Figure 1 Partial floor framing A section through the joists is shown in Figure 2. The thickness of the concrete floor slab is 41/2 ". It is reinforced with #3 bars spaced at 6" o.c. in the direction parallel with the concrete joists. The bottom of each joist is reinforced with 1#8 bar. The distance between adjacent joist webs is 30 ". The side of each joist is tapered at a slope of 1 and 12.
Figure 2. Section through concrete joist framing All concrete joists are constructed monolithically with the concrete slab and girders. For this reason, the joists are continuous span members and have both negative and positive bending moments. Maximum negative moment occurs at the face of each girder-joist connection and maximum positive moment occurs at midspan. Instead of completing a structural analysis using influence diagrams to find these moments, ACl allows analysis using the ACl coefficients contained in Table 6.5.2. To find the maximum moment, multiply the ACl coefficient Cm by the uniform floor load and the square of the clear span where Mu=Cm∗wu∗ln∧2.ACl coefficients for the concrete floor joists are shown in Figure 3. AClMc Figure 3. ACl load coefficients for concrete floor joists