Analysis and design of R/C tube structures in seismic regions.

摘要

The adequacy and feasibility of reinforced concrete (RC) tubular structures, designed to current building codes, in high seismic regions are studied. The basic configuration examined was a 31 story RC structure having a square plan of 11 bays at 8.9 feet on a side. The following five variations were considered: (1) Normal strength concrete (NSC) framed tube. (2) High Strength concrete (HSC) framed tube. (3) NSC braced tube. (4) HSC braced tube. (5) HSC braced tube, with selective prestressed braces.;For preliminary analysis, a simplified method, "an equivalent continuum of thin-walled tube" was used to estimate member stresses and structural displacement. A dominant parameter in this model shows that the tubular model is valid only for structures with a large slenderness ratio.;The structures were evaluated for static, service, and seismic safety conditions. Structural linear analysis and structural design were conducted for a three-dimensional model. Linear results for a two-dimensional model were compared to those of the three-dimensional model to evaluate the adequacy of two-dimensional model for use in the nonlinear analyses.;To study soil-structure interaction effects, the NSC Framed tube and the NSC braced tube were modeled seismically for different soils and ground motions. In this approach, the impedance functions of piles embedded in a layered media were developed using the matrix stiffness method.;The analysis results and general conclusions are as follows: Axial loading predominates in the column designs showing that the tubular behavior for the five designed structures is adequate. The HSC braced tube with selective prestressed braces provides an efficient way to eliminate shear lag behavior and appears more economical in material and stronger, thus more safe, compared to the other four designed structures. The tubular configuration confines most of the inelastic deformation to the girders ensuring strong column-weak beam behavior. Inclusion of soil-structure interaction may increase or decrease the seismic response. The seismic performance for the designed structures shows that current code requirements are adequate for safety conditions. However, the provisions need to be modified for future design to avoid structural damage under service seismic conditions.