Civil Engineering Reference
In-Depth Information
Chapter 6
Numerical Analysis of Instrumented RFERS
Abstract.
This chapter presents the finite element analysis of the building
monitored in Chapters 4 and 5. A plane strain model was employed through
dividing the column properties by the tributary width of the frame, and utilizing
the equivalent area and moment of inertia per foot of length of the waffle slab.
The analysis confirms many of the results gleaned from the discrete
instrumentation measurements. In particular, the lateral earth pressure exerted on
the rigid frame developed during the thermal expansion cycles is considerably
larger than the lateral earth pressure at rest.
6.1 Introduction
A 2-dimensional plain-strain finite element analysis of the longitudinal rigid frame
located along column line D (see Fig. 4.2) was performed. The frame is located
approximately at the center of the structure, and has a tributary width for soil load
of nearly 9.5 m. The finite element model included the northern wall of the
structure, and the nine columns and waffle-slab elements composing the rest of the
rigid frame. The structural elements were modeled to accommodate the plane
strain limitations of the model, through dividing the column properties by the
tributary width of the frame, and utilizing the equivalent area and moment of
inertia per foot of length of the waffle slab. This modeling of the waffle slab
assumes that the effective width of the slab engaged in resisting the lateral loads is
equal to the sum of half the distances between the frame along line D and the two
adjacent frames on opposite sides. This allows acceptable modeling of the lateral
stiffness of the moment frame, coupled with accurate modeling of the area of the
slab subject to volumetric temperature strains. Furthermore, to account for the
long-term load duration effects on the concrete elements and the presence of
cracked regions along the length of said members, the section properties of the
wall, columns and slab were reduced by 75 percent. This reduction is smaller than
that recommended by the Building Code Requirements for Structural Concrete
(ACI 318), but the actual field survey of the structural elements does not warrant a
further reduction.
