The figure shows a pile cap supported on two 18 inch square piles, The piles are

Question

The figure shows a pile cap supported on two 18 inch square piles, The piles are each provided with four #9 dowels with standard 90 degree bends for anchorage into the pile cap. The dowels are not epoxy coated, Because of the large moment applied 10 the pile cap, Pile A dowels must develop their full yield strength in tension, while Pile B dowels must develop their full yield stress in compression, If the piles are embedded 3 inches into the bottom of the pile cap, and the top and side clear cover to the dowels all exceed 3 inches. answer the following questions.Use Normal Weight Concrete With f_c' = 5000 psi and f_y =60,000 psi. Determine the development length, l_dh,required for pile A. Determine the development lenth,Idc, required for A what is the minimum thickness of pile cap n,to satisfy these requirement

Explanation / Answer

The design is based on the reinforcement attaining the yield stress, so the reinforcement must be properly bonded to the concrete for a finite length in order not to slip. This sufficient length to anchor bars near the end of connections is referred to as the development length, ld. The development length equation according to ACI 318 is presented here:

where:

db, The bar diameter

cb, The bar radius

t, Modifier for reinforcement location , 1.3 for top bars, 1.0 for other bars

e, modifier for epoxy coated bars

1.5 when cover < 3db or clear spacing < 6db

1.2 for other epoxy coated reinforcing

1.0 for non-epoxy coated reinforcing

The product, te, should not exceed 1.7

s, Modifier for bar size

0.8 for #6 and smaller

1.0 for #7 and larger

l, Modifier for lightweight concrete

1.3 for lightweight concrete

1.0 for other concrete

Ktr, transverse reinforcement index. According to ACI 318:

where:

Atr = total cross sectional area of all transverse reinforcement which is within the spacing, s, and which crosses the potential plane of splitting through the reinforcement being developed.

fyt = the yield strength of the transverse reinforcing

s = maximum C-C spacing of transverse reinforcement within the development length

n = number of longitudinal bars being developed along the plane of splitting.

Development Length in Tension

With the proper bar to bar spacing and cover, the common development length equations are:

#6 bars and smaller: or 12 in. minimum

#7 bars and larger: or 12 in. minimum

Development Length in Compression

Hook Bends and Extensions

The minimum hook length is:

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