A dissertation submitted in Partial requirements

Abstract

This study is concerned with the axle loads in Sudan, which is one of the important factors in highway and bridge design. Also it can be the starting point to perform a scientific research that lead to the Sudanese standard specifications for loads on highway bridges. Most bridges in Sudan are designed according to B.S standards. During the last few years, heavy trucks with multi-axles have entered Sudan and produced serious damages in highways. The National Highway Authority issued a law that restricts both axle and gross weights in Sudan for all truck categories, which are classified according to their axle arrangements. A permit to exceed the gross weight limitation 15% for limited duration for economical reasons is on the way. This study was carried during this period. In this study, loaded trucks are selected from every truck category and axles are weighted individually to determine the axle load for every selected truck. The sum of axles loads was compared with the gross weight and the portion of the gross weight that carried by each axle was evaluated. According to this ratio, the gross weight of each truck that passed Portsudan- Khartoum road in December 2002 had been recorded and distributed over the axles. Trucks with greatest gross weights that used Portsudan- Khartoum road in that month are selected for all truck categories. The load from these trucks were used in the analysis of a simple support bridge with different span lengths and girders spacing. The maximum bending moments and shear forces are calculated on the girders and compared with HA and HB loads. From the analysis of the data that are collected the allowable gross weights that are recommended by NHA are smaller than that required to satisfy the allowable axle loads. HB 30 units is the design live load for most highway bridges in Sudan. From the results this load give a safe design, for simple supported bridges with girders, only when girder spacing equal 1.25m. Truck shown in Fig. (4.23) give the most maximum stresses in the simple supported beams with different span lengths and girders spacing thus the author recommend this type to be the Sudanese design truck for highway bridges. In the future, the same study can be extend after 2004 when there will not be any permission in the allowable gross weights. Also future studies can be carried out by collecting more data and by using standards other than B.S 5400 on continues highway bridges.