Non-Destructive Evaluation of Gravity Load Carrying Capacity and Lateral Load Damage

The objective of this study was to develop a procedure to quantify the load carrying capacity of a slab-column connection as a function of the structural damage. To fulfill this objective, guidelines for damage assessment of reinforced concrete flat-plate buildings were developed. The intent of the guidelines was to assist engineers assess lateral load damage in the field and estimate the gravity load carrying capacity of the slab-column connection after an earthquake.

The relationship between gravity load carrying capacity and degree of lateral load damage was studied in laboratory. Gravity load tests were conducted on four slab-column connections and lateral load tests on five slab-column connections. It was found that when the degree of damage was slight to moderate, there was no reduction in the gravity-load-carrying-capacity of the connection. However, when the degree of damage was severe, a reduction in the gravity load carrying capacity should be expected.

The degree of lateral load damage was defined into four categories (slight, low, moderate and severe) and was characterized by the extent of cracking, stiffness degradation and yielding of the reinforcement in the slab-column connection. The degree of lateral load damage was also a function of the lateral drift level experienced by the structure.

Four assessment techniques were utilized to infer the lateral drift level. The techniques were based on results from visual observations and non-destructive testing conducted on four slab-column connections. Slab vertical deflection, crack density, crack depth, extent of areas of concrete delamination, and Seismic Wave Attenuation (SWA) measurements provided useful information for estimating the amount of damage due to cycles of lateral drift. The SWA method is a non-destructive method that has not been used previously for assessing damage in slab structures.

The guidelines provide an empirical approach for estimating the gravity load carrying capacity of a slab-column connection based on three steps: (1) assessment techniques for inferring the drift level experienced by the structure, (2) correlation of the inferred drift level with the degree of lateral load damage, and (3) estimation of the gravity load carrying capacity of the connection based on the degree of lateral load damage.