808 Calculation of the cross-tensioned slabs of wood

Published: 11 June 2010

The project's aim is to find a production adapted methodology of calculation of cross-tensioned slabs.

Area: Industrial wood construction
Budget: 200,000 SEK
Timetable: May 2010 - December 2011
Project Manager: Peter Jacobson, Martinson wooden bridges

Background

Cross Tense slabs of wood used today mainly in timber bridges, but can also be used as bjälklag.Vid design of cross-tensioned slabs to bridges that have an American computational model called "Ritter" used so far. The model was developed based on practical experiments with American woods. The model is something of a black box where the background of many factors is unknown. When using the model for many of the bridges we do today in Sweden, which is long and narrow, so extrapolating the model diagrams. The model used many times at the limit of its validity range, the model is not enough anymore. The model's empirical background makes it difficult to understand, and its validity is questioned attt by the SRA and Banverket. Unless Ritter model can be used is really no other option today. The need for a new calculation method is therefore very high.

Plates load carrying capacity based on the beams, which plate consists of are clamped only with the clamping force and the load is distributed between the beams by friction. The clamping force is very important to hold together and to the plate its load bearing capacity. Previously, the idea has been to slip between the beams does not occur at low loads without sliding completely prevented by having a high clamping force and slippage occurs only at high loads just before failure. Made tests and calculations in previous TCN-funded project "Wooden bridges for Rail" shows that shear stresses due to torque the plate gives slippage between the beams in the plate even at low loads. A test shows that these small shifts do not lead to immediate offense but give the plate a small permanent deformation upon unloading. The consequences otherwise of this drift, for example cyclic loading is largely unknown.

Purpose

The project's aim is to find a production adapted methodology of calculation of cross-tensioned slabs. There is a need for computational models for cross-tensioned slabs on different levels. First, a simple, quick and rough way to dimension mhatex. charts but partly also more sophisticated models to predict crimes and behavior just prior offenses. Simple elastic modeling for designing cross-tensioned slabs do not account for slippage. Advanced nonlinear elastic-plastic modeling can take into account slippage but the calculations are complicated.

The goal is to find out how accurate the results to be expected in calculations at different levels and to establish an appropriate material parameters for the different calculation models. The project aims also to using a plastic verified computational model building knowledge about how tensions from a purely elastic calculation can be equalized. So how can the plastic behavior considered in an elastic model.

The goal is not to produce a verified computational model because we only have a rupture test to work toward the calculation .. However, verification is expected to be made later through collaboration with another PhD project at Chalmers where more tests are planned broplattor

Final Report