Strut-and-tie modeling - Computational Analysis and Design of Bridge Structures - page 410

13.2.2 representative pile-supported footing
This hand-calculation example is illustrated in the final report of NCHRP
Project 20-07 Task 217 (Martin and Sanders 2007). Figure 13.10a depicts
a 3.3 m × 3.3 m × 0.9 m (11′ × 11′ × 3′) footing supported by nine piles
arranged in a 3 × 3 pattern. The total factored loading, including the
pile cap and the soil overburden, was 5164 kN (1161 kip) with a trans-
verse moment of 521 kN-m (384 kip-ft). The concrete used in the original
design had an f c ′ of 20.7 MPa (3000 psi), and the steel used was grade 60

1161 kip

384 kip-ft

Square column
3′ 6′′ × 3′ 6′′

2′ 3′′ 1′ 6′′

1′ 6′′ 2′ 3′′

11′ 0′′ × 11′ 0′′ × 3′ 0′′-thick pile cap

18 no. 8
each way

2′ 4′′

2′′

6′′

14′ × 14′′
precast
pile

4′ 0′′ 4′ 0′′

(a)

1/6 × 3.5′′ = 0.583′′

2′ 3′′ 1′ 2′′ 1′ 2′′

145 kip (typ.)

2′′

Q

M

R

2′ 2′′

37.4°
190 kip

190 kip

H D

2′′

6′′

145 kip (typ.)

4′ 0′′ 4′ 0′′

(b)

Figure 13.10 (a) Details of the existing footing. (b) Section through the centerline of
footing. (Continued)