Post Earthquake Evaluation of Axial Forces and Boundary Conditions for High-Tension Bars


Abstract eng:
High-tension bars or cables, such as diagonal braces of a truss, cables of a bridge, struts of a space structure, tie-bars of an arch, various anchorage cable and rods, usually play an important role in a civil structure. Identification of axial forces in these members is critical to post earthquake damage assessment of the structure. In view of the increasing uncertainty in boundary conditions due to seismic damage, two analytical methods assuming that the member is an Euler-Bernoulli beam or a Timoshenko beam are examined for rapid estimation of axial forces in high-tension bars based on dynamic testing. Bending stiffness effects are taken into account. Using the dynamic measurements from five or more sensors, the methods are able to identify the axial force in the bar and to determine the damage degree of the supports at two ends. Numerical studies based on finite element methods are conducted for a single beam member, considering different parameters with regard to the effect of bending stiffness, slenderness ratio and boundary condition, to compare the effectiveness of the two methods in a wide range of situations. It turns out that the two methods are more suitable for the lower values of the non-dimensional parameter ξ for bending stiffness. When ξ<30, both methods can achieve good estimation with high accuracy. On the other hand, the estimation error of the Euler beam based method rapidly increases with the decrease of the slenderness ratio till the value of 20. The Timoshenko beam based method, comparatively, is quite steady and completely independent of this parameter. A more complex externally prestressed structure is then simulated to investigate the feasibility of the methods by using both global and local modes. It is validated that all the cable tension estimations have been achieved with high accuracy. The estimation errors are less than 5%. Laboratory experiments are carried out to validate the applicability and accuracy of the two methods. A steel bar is fixed at both ends onto the loading device and loaded increasingly by uniaxial tension. Using the frequencies and mode shapes identified by modal tests, the axial forces as well as the boundary conditions of the specimen are determined based on the two methods. It has been validated that most identified axial forces achieve a satisfied accuracy with a relative error below 10%. All the identified boundary stiffness approaches infinite, consistent with the actual fixed end.

Contributors:
Conference Title:
Conference Title:
16th World Conference on Earthquake Engineering
Conference Venue:
Santiago (CL)
Conference Dates:
2017-01-09 / 2017-01-13
Rights:
Text je chráněný podle autorského zákona č. 121/2000 Sb.



Record appears in:



 Record created 2017-01-18, last modified 2017-01-18


Original version of the author's contribution as presented on USB, paper 312.:
Download fulltext
PDF

Rate this document:

Rate this document:
1
2
3
 
(Not yet reviewed)