Bridge load testing can answer a variety of questions about bridge behavior that cannot be answered otherwise. The current governing codes and guidelines for bridge load testing in the United States are the 1998 NCHRP Manual for Bridge Rating through Load Testing and Chapter 8 of the AASHTO Manual for Bridge Evaluation. Over the last two decades, the practice of load testing has evolved, and its intersections with other fields have expanded. The outcomes of load tests have been used to keep bridges open cost-effectively without unnecessarily restricting legal loads, when theoretical analyses cannot yield insights representative of in-service performance. Load testing data can be further used to develop field-verified finite-element models of tested bridges to understand these structures better. In addition, structural reliability concepts can be used to estimate the probability of failure based on the results of load tests, and noncontact measurement techniques capturing large surfaces of bridges allow for better monitoring of structural responses. Given these developments, a new Transportation Research Board (TRB) Circular, Primer on Bridge Load Testing, has been developed. This document contains new proposals for interpreting the results of diagnostic load tests, loading protocols, and the determination of bridge load ratings based on the results of proof load tests. In addition, included provisions provide an estimation of the resulting reliability index and the remaining service life of a bridge based on load testing results. The benefit of load testing is illustrated based on a cost–benefit analysis. The current state-of-the-practice has demonstrated that load testing is an effective means for answering many important questions regarding bridge behavior that are critical to decisions on bridge maintenance or replacement. Load testing has evolved over its history, and the newly developed TRB Circular reflects this evolution in a practical way.

Adding steel fibers to concrete improves the capacity in tension-driven failure modes. An example is the shear capacity in steel fiber reinforced concrete (SFRC) beams with longitudinal reinforcement and without shear reinforcement. Since no mechanical models exist that can fully describe the behavior of SFRC beams without shear reinforcement failing in shear, a number of empirical equations have been suggested in the past. This paper compiles the existing empirical equations and code provisions for the prediction of the shear capacity of SFRC beams failing in shear as well as a database of 488 experiments reported in the literature. The experimental shear capacities from the database are then compared to the prediction equations. This comparison shows a large scatter on the ratio of experimental to predicted values. The practice of defining the tensile strength of SFRC based on different experiments internationally makes the comparison difficult. For design purposes, the code prediction methods based on the Eurocode shear expression provide reasonable results (with coefficients of variation on the ratio tested/predicted shear capacities of 27–29%). None of the currently available methods properly describe the behavior of SFRC beams failing in shear. As such, this work shows the need for studies that address the different shear-carrying mechanisms in SFRC and its crack kinematics.

Upon assessment of existing reinforced concrete short-span solid slab bridges according to the recently implemented Eurocodes that include more conservative shear capacity provisions and heavier axle loads, a number of these structures were found to be shear-critical. The results from recent experimental research on the shear capacity of slabs indicate that slabs benefit from transverse load distribution. Recommendations for the assessment of solid slab bridges in shear are developed on the basis of these experiments. A load spreading method for the concentrated loads is proposed and the applicability of superposition of loading is studied. The resulting most unfavourable position for the design trucks is provided and implemented in the so-called Dutch "Quick Scan" method (QS-EC2). Cases of existing bridges are studied with the previously used QS-VBC as well as with the QS-EC2 that includes the recommendations. As a result of the assumed transverse load distribution, the shear stress to be considered at the support based on the recommendations becomes smaller.

For shear-critical structural elements where the use of stirrups is not desirable, such as slabs or beams with reinforcement congestion, steel fibers can be used as shear reinforcement. The contribution of the steel fibers to the shear capacity lies in the action of the steel fibers bridging the shear crack, which increases the shear capacity and prevents a brittle failure mode. This study evaluates the effect of the amount of fibers in a concrete mix on the shear capacity of steel fiber-reinforced concrete beams with mild steel tension reinforcement and without stirrups. For this purpose, 10 beams were tested. Five different fiber volume fractions were studied: 0.0%, 0.3%, 0.6%, 0.9%, and 1.2%. For each different steel fiber concrete mix, the concrete compressive strength was determined on cylinders and the tensile strength was determined in a flexural test on beam specimens. Additionally, the influence of fibers on the shear capacity was analyzed based on results reported in the literature, as well as based on the expressions derived for estimating the shear capacity of steel fiber-reinforced concrete beams. The outcome of these experiments is that a fiber percentage of 1.2% or fiber factor of 0.96 can be used to replace minimum stirrups according to ACI 318-14 and a 0.6% fiber volume fraction or fiber factor of 0.48 to replace minimum stirrups according to Eurocode 2. A fiber percentage of 1.2% or fiber factor of 0.96 was observed to change the failure mode from shear failure to flexural failure. The results of this study support the inclusion of provisions for steel fiber-reinforced concrete in building codes and provides recommendations for inclusion in ACI 318-14 and Eurocode 2, so that a wider adoption of steel fiber reinforced concrete can be achieved in the construction industry.

Nowadays, with the aging of the bridges and the advancements in technology, load testing has emerged as an effective method to assess existing concrete bridges with missing information, or where analytical methods do not provide an accurate assessment. Two types of load tests are identified: diagnostic load tests and proof load tests. Both rely on field measurements of parameters or structural responses of the bridge during the test. A diagnostic load test measures the response of the bridge so that analytical models can be calibrated and evaluated. In a proof load test, the bridge directly demonstrates that it can carry a certain load. Since large loads are applied, the bridge needs to be carefully monitored. In this case, monitoring the measurements provide a warning to avoid damage. This paper reviews the literature on reported load tests and the measurement techniques used during these tests. It also includes a review of traditional and recently developed sensing technologies. Finally, the measurement requirements for diagnostic and proof load tests are given as well as a flow chart to guide engineers in the selection process of appropriate monitoring and measurement techniques during load tests. This paper can serve engineers during the preparation of a load test.