April 16, 1998

VARIABILITY OF DEFLECTIONS OF REINFORCED CONCRETE BEAMS

by:

Bong-Seob Choi, Graduate Student

Department of Civil & Environmental Engineering

The Pennsylvania State University

ABSTRACT

In the design of reinforced concrete structures, safety is the most important limit state but serviceability must also be satisfied for appropriate design. Serviceability usually refers to control of deflections and crack widths at service loads. This presentation deals with the control of deflections.

In the current ACI 318-95 Code, there are two methods to control deflections. The first one is to use the indirect method of minimum thickness. The second one is to directly calculate deflections within the maximum allowable values specified in ACI Code if the minimum thickness value is not satisfied. However, the current minimum thickness values are limited for application to a range of design conditions. The direct calculation of deflections also has high variability between measured and computed results for instantaneous as well as long-time loading conditions.

Results of a parametric study are presented to evaluate the validity of the current minimum thickness values. To do so, an algorithm based on ACI 318 procedure was developed to calculate minimum thickness values. For variability analysis of deflections, a deterministic layered beam model, which can also analyze non-linear problems due to cracking and time-dependent effects was developed, and the calculated deflections were compared with the experimental beam data to verify this model. Finally, Monte Carlo Simulation Technique will later be used for quantitative evaluation of variability.