ENGINEERING COURSEWORK

Engineering Coursework: Effect of Section Shape on the Load Carrying Capacity of Beams





Abstract

This paper investigates the effect of moment transfer efficiency of a beam web on deformation capacity at beam-to-column connections. Non-linear finite element analysis of five connection models was conducted. Analytical results showed that the moment transfer efficiency of the connection with a box column was poor when compared to a connection with an H-column; this was due to the out-of-plane deformation of the column flange. Based on previous test data, analytical results were compared with experimental results. Analytical and experimental results showed that the deformation capacity of the connection with a box column decreased due to the poor moment transfer efficiency of a beam web, followed by strain concentration at the beam flange.

Keywords: Box column; Moment transfer efficiency; Strain concentration; Deformation capacity

Engineering coursework: Effect of Section Shape on the Load Carrying Capacity of Beams

Introduction

Generally, a beam resists transverse loads by bending action. In a typical building frame, main beams are employed to span between adjacent columns; secondary beams when used - transmit the floor loading on to the main beams. In general, it is necessary to consider only the bending effects in such cases, any torsional loading effects being relatively insignificant. Under increasing transverse loads, beams of category would attain their full plastic moment capacity. This type of behaviour has been covered in an earlier chapter. Two important assumptions have been made therein to achieve this ideal beam behaviour. They are:

The compression flange of the beam is restrained from moving laterally, and

Any form of local buckling is prevented.

If the laterally unrestrained length of the compression flange of the beam is relatively long as in category 2 of Table 1, then a phenomenon, known as lateral buckling or lateral torsional buckling of the beam may take place. The beam would fail well before it could attain its full moment capacity. This phenomenon has a close similarity to the Euler buckling of columns, triggering collapse before attaining its squash load (full compressive yield load).

Lateral buckling of beams has to be accounted for at all stages of construction, to eliminate the possibility of premature collapse of the structure or component. For example, in the construction of steel-concrete composite buildings, steel beams are designed to attain their full moment capacity based on the assumption that the flooring would provide the necessary lateral restraint to the beams. However, during the erection stage of the structure, beams may not receive as much lateral support from the floors as they get after the concrete hardens. Hence, at this stage, they are prone to lateral buckling, which has to be consciously prevented.

Typically, Japanese steel moment resisting frames have a square hollow section that is used for the columns, and an H-shaped section that is used for the beams. A square tube column has two webs at each side, but no web in the center where the beam web is connected. This is different from the US connection, which has a web at ...