An influence of technological contraflexure of crane bridges on its durability

Standard requirements till 1996 year during bridge crane manufacturing demanded a positive technological contraflexure. As a result of this process were implemented technological compressive stress into tensile zone from inertial and operational loads and tensile stress into compressive zone. This way there were redistributed resultant stress which have increased fatigue strength of exploited crane bridges. Actually valid standard PN-ISO 7363 has removed this obligatory requirement. Its use depends of crane buyer demands. Reduction of initial positive deflection can be seen after few years of crane operations. It is a case of girders permanent deflections increment. Article presents method of technological prestressing of bridge girders with its practical application to obtain positive contrafexure

Emergency diagnostics of load-carrying structures into the works transport

Sudden increase of exploited cranes since 1970 year and implementation of European standards restricting safety factors ware cause of many breakdowns and accidents. That’s why act about technical supervision from 2000 year impose checkups of technical conditions of supporting structures every 12 months. Checkups include also welded joint and crane tracks. Aim of routine test is to find out if there are no damages which may affect on constructions safe exploitation. Routine tests give information if construction can be exploited. Article presents methodology of diagnostics inspection for defect detection of constructions and its practical application