Last fall, I attended IALCCE 2018 where together with my colleagues from TU Delft, I organized a Mini Symposium on Load Testing of New and Existing Structures.
For this MS, I submitted 4 papers as coauthor – 3 of these papers are the results of projects with B.Sc. thesis students from USFQ funded by my 2016 Chancellor Grant. During the MS, I presented my work on stop criteria and I also presented about diagnostic load testing of steel bridges on behalf of ADSTREN.
The abstracts of the papers are:
Proposed stop criteria for proof load testing of concrete bridges and verification
Eva Lantsoght, Cor van der Veen, Dick Hordijk
In a proof load test, a load representative of the factored live load is applied to the bridge. Since the applied load is large, stop criteria are important. Stop criteria for shear and flexure are proposed based on existing codes and guidelines, laboratory experiments, and theoretical considerations. This proposal is verified with the results from pilot proof load tests. The result of this comparison is that the stop criteria are never exceeded, or that they are exceeded only in the last load step. The proposed stop criteria are thus not overly conservative for application to field testing. However, information about the available margin of safety is not always available, especially for shear failures, and will need further experimental validation.
Nonlinear finite element analysis of beam experiments for stop criteria
Jose Eduardo Paredes, Eva Lantsoght
Proof load testing is used to assess the structural capacity of existing bridges. Stop criteria, based on measurements taken during proof load tests, determine if a test should be stopped before reaching the target proof load in order to maintain structural integrity. A nonlinear finite element model is proposed to investigate stop criteria. A reinforced concrete beam with plain reinforcement is modeled. The goal is to develop a reliable finite element model with adequate material constitutive models to analyze available stop criteria from existing codes. The beam experiment is verified in terms of strains. Stop criteria from ACI 437.2M-13 and the German guideline are analyzed for the beam model. The presented analysis shows that nonlinear finite element models can be used for the evaluation of stop criteria for proof load testing to limit the required number of laboratory tests.
Development of a stop criterion for load tests based on the critical shear displacement theory
Kevin Benitez, Eva Lantsoght, Yuguang Yang
The capacity of existing bridges is an important aspect regarding the safety of the traveling public.
Proof load testing can be a useful option to evaluate if an existing bridge satisfies the requirements from the code. The stop criteria provided by the Guidelines are generally suitable for flexure only. Therefore, in this paper, shear is considered. When developing a stop criterion for shear for proof load tests on existing bridges, many different approaches could be taken. Here, a stop criterion is developed based on the Critical Shear Displacement Theory. The development of the stop criterion is based on the analysis of the contribution of each of the mechanisms of shear transfer. The criterion is verified with experiments on beams in the laboratory. The consequence of this development is that now a stop criterion for shear with a theoretical basis is provided.
Verification of flexural stop criteria for proof load tests on concrete bridges based on beam experiments
Andres Rodriguez, Eva Lantsoght
When performing proof load tests, irreversible damage may occur. Guidelines for performing the test have been developed, which establish stop criteria to terminate the test before this happens. The stop criteria prescribed in the currently available codes are mainly designed for buildings, but load tests are also performed on bridges. This investigation compares the results from beams tested in the laboratory with stop criteria and analyzes their applicability on reinforced concrete bridges. The stop criteria from ACI 437.2M-13, the German guideline of the DAfStB, and a proposal developed by Werner Vos from TU Delft were evaluated. It was found that the DAfStB concrete strain stop criterion provided the most consistent results. The ACI stop criteria should only be applied if the ACI loading protocol is being followed. The deflection proposal by Vos, seems to be a reliable option, but further investigation needs to be done before it can be applied.
The slides of the presentations are: