After a brief summary of the contents of the SP and the examples, several general points are discussed which are based on observations made about the examples. The choice of a strut-and-tie model is a major issue and different engineers may propose various modles for the same task. This leads to a discussion of the uniqueness of models and whether it is acceptable that different engineers may choose different models and thus different reinforcement arrangements and detailing for the same D-region. A further issue identified in some of the examples was the transition of a B-region to a D-region, and the procedure of modeling is shown. Finally the role and the importance of detailing is emphasized and some examples for this are given. Also some observations are made which led to recommendations for reconsidering some code provisions.

A double corbel projecting from an interior column is designed using the strut-and-tie method according to ACI 318-02 Appendix A. The corbel transfers precast beam reaction forces, Vu of 61.8 kips (275 kN) acting at 6 in. (152 mm) from the face of the column at both ends. To account for beam creep and shrinkage deformations, a factored horizontal force, Nuc of 14.3 kips (63.6 kN) is assumed to develop at each side of the corbel top. The column is 14 in. (356 mm) square. The upper column carries a factored compressive axial load, Pu of 275 kips (1223 kN). The compressive strength of concrete, fc and yield strength of steel reinforcement, fy are taken as 4 ksi (27.6 MPa) and 60 ksi (414 MPa), respectively. Normal-weight concrete is assumed. The selected dimensions including the bearing plates are shown in Fig. (3.2-2). The shear span to depth ratio, a/d, is 0.38. A simple strut-and-tie model shown in Fig. (3.2-3) was used for the design. The provided main tie reinforcement is 7 #4 (#13 mm) bars. The anchorage of these bars is provided by welding each end of the bars to a structural steel angle of 4 in. x 4 in, x 1/2 in. (102 mm x 102 mm x 13 mm). The reinforcement details are shown in Fig. (3.2-5).

Strut-and-tie models make the design of portions of complex structures transparent. This example, a pier table from a cable stayed bridge, is developed to show how strut-and-tie modeling can be used for an area that may be exposed to cyclic loading and how the results from alternate loads may be superimposed upon one another. The pier table transmits forces from the pylon, through an integral superstructure connection, to individual support legs. The pier table also creates an area for the transmission of superstructure forces. This example briefly describes the model development based upon the perceived flow of forces within the structure. The tie reinforcement is then detailed and the nodal zones checked.

A 20 ft (6.10 m) span deep beam was designed using the strut-and-tie method according to ACI 318-02 Appendix A. The beam is 20 in. (508 mm) wide and 80 in. (2032 mm) deep and carries two concentrated factored loads, V, of 360 kips (1601 kN) each. Bearing plates of 18 in. x 20 in. (457 mm x 508 mm) are provided at all loading and support locations. The self-weight was not considered in the design. The compressive strength of concrete, fc and the yield strength of the steel reinforcement, fy are taken as 4 ksi (27.6 MPa) and 60 ksi (414 MPa), respectively. A simple strut-and-tie model shown in Fig. (1 b-2) is used in the design. The provided reinforcement for the main tie is 2 layers of 5 #9 (#29 mm) bars. The anchorages of these bars are provided by means of standard 90’ hooks. The reinforcement details are shown in Fig. (1 b-6).