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Abstract

Structures designed to withstand pedestrian movement such as bridges, slabs and grandstand are sometimes exposed to high temperature due to fire and other environmental factors. The ability of structure to withstand dynamic load without collapse or unfavourable deformation is largely dependent on its dynamic properties. This research aims to investigate the changes that occur in dynamic properties such as natural frequency, mode shapes, damping parameters when a steel structure is exposed to fire using LUSAS finite element software. The research also looks to explore the changes in dynamic response (acceleration and mid stress) of a simple pedestrian steel deck under the influence of different types of dynamic load from human movement and fire conditions.
This research adopts the use of LUSAS finite element to model a steel flat bridge deck with material properties assigned to represent the changes in young’s modulus of steel that occurs from room temperature of 20oC to 1200oC. Eigenvalue frequency analysis was carried out to obtain the dynamic properties of the structure at different temperature. After which steady state dynamic analysis was performed on the model to obtain dynamic response in acceleration and mid stress using different types of human loading.
The results obtained from the eigen analysis on LUSAS gave some values of natural frequencies and mode shape of the finite element model at different temperature. It was concluded that heat and temperature increase do not affect the mode shape of structure, but natural frequency of mode shapes decreases proportionally as the young’s modulus of the steel material decreases. It also was discovered that the mass damping parameter decreases proportionally with increase in temperature but stiffness damping parameter increases proportionally with increase in temperature.
The results from steady state dynamic analysis helped us to evaluate the intensity of walking and running load in a pedestrian footbridge structure in crowded condition. It was concluded that walking load is more intense at frequencies between 0.5 to 1.5Hz, while running load is more intense in structure from 1.5Hz and above.
The parametric study of steady state response using different types of human load at elevated temperature enabled us to ascertain the changes in vertical acceleration and mid stress in the model considering different frequencies and load types . It was concluded that dynamic response in structure is governed by the dynamic load intensity from the fact that the vertical acceleration in the model increases as the dynamic load increases. It was also observed that the dynamic load is dependent on the type of human movement and the natural frequency of the structure

Course: Civil Engineering - MSc - C0618

Date Deposited: 2025-01-16

URI/permalink: https://library.port.ac.uk/dissert/dis14662.html