MEASUREMENT PLAN AND ESTIMATION OF TEMPERATURE EFFECTS IN THE CONCRETE PEDESTRIAN BRIDGE

摘要

The bridge structures exposed to atmosphere are subjected to an exchange of heat energy between the surfaces of structure and the environment. The interaction between the elements of the structure and the climatologically environment results in temperature differences between the elements of structure. These temperature differences produce strains and deformations in the restrained structures. EN 1991-1-5 is European standard that defines thermal action to buildings and girder bridges. However, there are not data for arched, framed, suspension and cable stayed bridges. In order to analyze these bridge types, EN 1991-1-5 suggests that appropriate values should be derived from specialist data, special studies or test results. This articulates that is necessary to perform experimental and theoretical researches of thermal actions effects on aforesaid types of bridges. Also, European standard EN 1991-1-5 suggested that many characteristic bridge temperature components should be specified in the National Annex. In order to better understand thermal effects on the bridge in Mediterranean climate, one pedestrian bridge in Podgorica is equipped for monitoring of temperature changes and strains. All instruments are embedded in structure during the construction of the bridge. In investigation, that is presented in this paper, the response of one the pedestrian concrete bridge is studied under environmental loads. Structure clear span between abutments is 28.0m. The width of the box is 1.5m with parallel webs. Height of the box varies from 0.9m in the middle part of the bridge to 2.45m on the abutments. Thicknesses of lower and upper slabs are varying from minimal 15cm in the middle of span to 80cm at abutments. Thickness of the box web is 20cm. In order to predict daily and long term temperature variations along the cross section of the bridge and temperature influence on stress, measurements on the pedestrian bridge were performed in five stages (two autumn and one wintry, spring and summer), during two days, with data recording in every 30 minutes. All measurement data are registered by TML data logger. TML type T thermocouples were used to measure temperature values into concrete box cross section. Strain on the concrete surface is measured by strain gauges type WFLM-60-11-2LT. Strain inside concrete is measured by embedded strain gauges type PMFL-60-2LT. Strain in the reinforcement is measured by strain gauges type PFL-30-11-3LT. Thermocouples and strain gauges are protected by PVC tube and PVC box which are guided to collected equipment boxes. Strain gauges of the type PFL-30-11- 3LT are protected by silicon coat. Thermocouples and strain gauges extension lead wires are guided with bee line to collected equipment boxes. There are seven equipment boxes in the bridge and their locations are qualified by measurement plan. Equipment boxes are protected by annihilation and they are accessible only for experimental usage. During the acquisition of data, it has been concluded that only one thermocouple, located in outer box of the cross section 1-1, has been damaged. All other thermocouples and strain gauges have steady measurements. Data acquisition is started in October, year 2006. The experimental part of research is finished at the end of June 2007. Based on this measurement we obtained own experimental data of temperatures and strains in the concrete box bridges in the Mediterranean climate.