Frames

1. INTRODUCTION

Frames of varying size and complexity represent one of the most frequent uses of structural steel. Whilst the most obvious application is in buildings, support frames for bridges, offshore platforms, falsework and temporary structures, and industrial storage systems also constitute a significant usage.

The main components of a rectangular arrangement are identified in Figure 1. Vertical loads on the roof and floors are transmitted by bending and shear into the columns, which, in turn, transfer load into the foundations by means of compressive, bending, and shearing actions. Horizontal loading, e.g. due to wind, must also be transferred into the foundations and may, depending upon the frame geometry and the relative magnitudes of the vertical and lateral loads, induce tension in some columns and, therefore, uplift on the foundations.

In general, a 3-dimensional building frame may be separated into a set of planar frames with well-defined support or restraint conditions for out-of-plane deformations (see Figure 1). These planar frames should be investigated for two different limit state conditions:

• ultimate limit state (ULS)
• serviceability limit state (SLS)

Details of these investigations are provided in later lectures. In this introductory lecture, attention is focused on describing the main aspects of frame behaviour and the ways in which these aspects are linked to various techniques for predicting structural response. The lecture is a preparation for later more detailed treatments.