Characterization of Structural Walls

This task consists of a fundamental research experimental program focused on the in-plane behavior of high-strength-concrete structural walls with boundary elements with the objective of determining their elastic and inelastic web-crushing capacity. These tests will provide the benchmark data required to establish performance limits for dependable ductile shear failure modes.

Structural walls confined by boundary elements are characterized by thin plane elements mainly carrying the in-plane loads and boundary elements that take most of the flexural force resultants. Such conditions are common in thin-webbed girders, flanged building walls, integral wall-panels for frame, and hollow box pier and girder sections. The approximate scale of the overall test unit dimensions is 1/4 and the typical cross-section is shown in Figure 1. The relative depth ratio, Dw/DB, where Dw is the depth of the structural wall only and DB is the depth of the boundary elements, is kept constant. Wall thickness and dimensions for the boundary element DB were selected based on prior research knowledge to create the conditions for web-crushing without allowing flexural or diagonal tension shear failures to occur first.

Figure 1. Cross-Section Geometry of Structural Wall Test Units

The parameters included in the experimental investigation are (1) the concrete compressive strength f’c and (2) the boundary element longitudinal reinforcement ratio. A series of eight structural walls with equal geometry are considered. Concrete with design compressive strengths at 28-days of 34, 69, 103, and 138 MPa (5, 10, 15, and 20 ksi) will be considered. Three different amounts of longitudinal reinforcement in the wall boundary elements will be considered order to ensure elastic and inelastic web-crushing failures. All test units will be subjected to a constant axial load level of 401 kN (90 kips) equal to 0.10f’cAg based on f’c = 34 MPa (5 ksi). This follows from the rationale that the load-bearing demands (i.e. dead load) on the element are not assumed to vary with their change in concrete strength.

Figure 2. Test Unit Response and Assessment

Preliminary analysis of the test units with rl = 0.0771 for different concrete strengths are shown in Figure 2 accompanied by the ACI design limit and the inelastic web-crushing assessment model developed by the co-PI. It can be seen that the ACI approach is very conservative and that adequate flexural response can be obtained by use of high-strength concrete. Transverse reinforcement in the wall will be designed to satisfy the UCSD three-component shear capacity equations, which assumes resistance from of a concrete Vc, axial-load Vp, and steel Vs components. The transverse reinforcement and spacing will be designed such that 0.85V = Vu.The transverse reinforcement details will be kept constant for all test units. Standard concrete and steel-reinforcement material tests will be conducted.

The test units will be loaded monotonically and cyclically according to a standard, incrementally increasing, fully-reversed cyclic pattern, with constant axial load. Two monotonic tests will also be conducted to evaluate the effects of crack closing misalignment on the onset of web crushing failure. An elevation and a rendering of the test setup and loading devices are shown in Figure 3 and Figure 4, respectively. All test units will be loaded both laterally and vertically by two independent loading systems, which will be measured through load.

Figure 3. Elevation of Single Structural Wall Test Setup

Figure 4. Rendering of Single Structural Wall Test Setup