ABSTRACT

Modelling of the mechanical properties of materials and structures is a complex subject. In some applications, the material can be assumed to be perfectly elastic, implying that all deformation caused by stresses are totally reversible. That assumption only applies to a limited range of materials, unlike the more realistic approach accounts forinelastic processes like plastic yielding or cracking. Plastic analysis of structures has been found in previous studies to be a more efficient and economical way of assessing civil engineering structures with ductile properties when compared to elastic theory. While elastic theory focuses on the load that causes yielding on the structure. Plastic theory shows that structures are able to withstand even higher loading than those responsible for yielding before formationof plastichinges and eventual collapse.

This study is uses The Incremental Method of plastic analysis to assess the case study. The bridge is modelled on the Solid works software program and analysis done on the ANSYS Software program and loading on the structure is incremented until a plastic hingeforms, and then until failure collapse. Illustrative examples are given to show how this working is done mathematically by hand for small components while modeling of the bridge and analysis of the case study is done on the ANSYS and Solid-Works software programs. The loading on the structure is estimated using Euro-code EN 1991-2:3 section 5 (Actions on footways, cycle tracks, and footbridges). Maximum pedestrian traffic isgotten by taking field measurements of number of people on the deck at a time over a period of 3 days at hours were traffic was expected to be maximum on the bridge. The average weight of the Nigerian adult is approximated from literatures available on the internet and used for crowd actionevaluation.

On Conclusion of field measurements and analysis: the average weight of the Nigerian adult was estimated to be 65.8kg (6.58N) per adult, maximum real life traffic on the Ugbowo pedestrian bridge is estimated to be 35 persons at a time, From analysis the maximum plastic stress was over 6.1683 x 10^7 Pa, The maximum deformation at this stress is gotten as 1.4815 x 10^-2m, Density 2300kg/m3, Drucker-Prager Strength Piece wise 4.4 x 10 ^7Pa, Maximum fracture energy 100Gf J m^-2, MaximumTensile Pressure -4.x 10^6Pa. The maximum strain remained zero at this stress this showed that the bridge deck remained in the elastic zone. This means that the deck would require loading considerably higher than loading currently applied to cause plastic deformation andfailure.