Load Testing & Evaluation of Two Swing Span Bridges

SDR was tasked to structurally evaluate two swing span bridges through load testing coupled with Finite Element Analysis (FEA) with the aim of removing the current load posting. The tested controlling spans comprised steel plate girder sowing span and CIP concrete slab spans. Test results revealed that, the actual performance of the test bridges is more favorable than what is estimated by design codes. Load rating of the controlling spans was revised considering test findings and FEA results, which resulted in removing the posting weight.

Load Testing & Evaluation of Five Fixed and Movable Bridges

SDR was tasked to evaluate five bridges located along Louisiana State Highway 82 through load testing coupled with Finite Element Analysis (FEA) with the aim of removing the current load posting. The tested controlling spans comprised low truss swing spans; plate girder swing spans; steel I-beam approach spans; CIP concrete slab approach spans; and precast concrete slab spans. Test results revealed that, the actual performance of the test bridges is more favorable than what is estimated by design codes. Load rating of the controlling spans was revised considering test findings and FEA results, which resulted in removing the posting weight.

STRUCTURAL EVALUATION OF RC T-BEAM BRIDGES THROUGH LOAD TESTING & FEA

Structural evaluation through load testing coupled with advanced Finite Element Analysis (FEA) is a powerful tool to load rate posted bridges with the aim of removing current postings. Based on SDR’s vast experience in structural evaluation and load testing, bridges can carry much higher loads than those estimated by design codes equations. Load testing captures actual behavior of the structure (load distribution) and accounts for strength enhancing factors not included in design

The load rating of LA 182 bridge over Berwick Bay is controlled by reinforced concrete T-beam spans. SDR was tasked with performing the structural evaluation though load testing of the T-beam spans with the aim of removing the current posting.
Test results and FEA reveal that, due to support conditions of the slab, partial fixed end moments are developed, causing significant reduction in mid-span moment compared to moment calculated assuming simple-beam action. Load rating of the bridge was carried out in consideration of the test findings and FEA results, resulting in an increase of load rating factor from 0.85 to 1.23.

LOAD TESTING OF LA-1 OVER LOCKPORT CANAL

Structural evaluation through load testing, coupled with advanced Finite Element Analysis (FEA) is a powerful tool to load rate posted bridges with the aim of removing current posting. Based on SDR’s vast experience in structural evaluation and load testing, bridges can carry much higher loads than those predicted by design codes. Load testing captures actual behavior of the structure (load distribution) and accounts for strength enhancing factors not included in design.

The LA-1 bridge over Lockport Canal was built in 1959. The bridge load rating is controlled by the reinforced concrete slab spans. SDR was tasked with performing the structural evaluation though load testing of the slab spans with the aim of removing the current posting.

Test results, along with the FEA, reveal that due to the support conditions of the slab, partial fixed end moments are developed, causing significant reduction in mid-span moment as compared to moment calculated assuming simple-beam action. The slab behaved in two-way bending action rather than the one-way bending action used in conventional design and load rating. Load rating of the bridge was carried out in consideration of the test findings and FEA results, which resulted in a load rating factor increase from 0.75 to 1.22.

US 61 AIRLINE HIGHWAY RAMP BRIDGE OVER I-10

US-61 ramp K over I-10 is located in Ascension Parish, LA. The curved ramp consists of five spans with a total length of 594 ft. The first four spans are continuous steel spans and the last span is a simple composite steel span. The bridge cross section consists of two built-up steel plate girders. The two steel girders support a concrete deck, which is also supported by floor beams that connect the two steel girders.

Span 2 of the bridge ramp was struck by an over-height vehicle that was traveling eastbound on I-10, causing damage between the two field splices. SDR was tasked with proposing a practical, safe, and cost-effective solution for the rehabilitation of girder B of the US-61 bridge. SDR performed field inspection of ramp K to identify any distress in the structural elements. In addition to field inspections, SDR developed refined 3-D and 2-D finite element models, based on as-built super structure drawings. Grillage models were used for the main girders and deck. FE analysis accounted for the current condition of the different structural elements as revealed by the field investigation.

In addition to modeling and field inspections, SDR performed structural evaluation through load testing. Sensors were installed at 6 locations along the length of girder A. Four vibration strain sensors were installed at different positions of the girder A cross section. Five independent truck positions were used to conduct the test.

SDR proposed total removal of the concrete deck within the damage segment of the bridge in addition to removal of the concrete deck between the field splices before replacing the damaged portion of the girder. SDR used Midas to model bridge conditions after removal of damaged girder between the two splices. Further, staged construction analysis was performed with FE models to assess the bridge condition during construction. Analysis showed that removal of the damaged portion of the girder and the concrete deck would not cause any structural damage; however, removal did present challenges in construction. Details for laying out the removal and replacement procedures were provided by SDR.

After installation of the span, SDR performed additional structural evaluation through load testing to compare conditions before and after removal of the damaged girder; the load testing was performed with identical sensor locations and truck positioning as compared to testing performed before removal. Stresses and strains were monitored in both evaluations to compare the change in behavior of the new girder.

BAYOU LAFOURCHE BRIDGE TESTING

The Bayou Lafourche Bridge is located on US 80 over the Bayou Lafourche Diversion Canal in Louisiana. This project adopted the innovative approach of Accelerated Bridge Construction (ABC) for rapid construction of precast concrete I-girder bridges and marks the first time this process was implemented in Louisiana. This bridge consists of six prestressed concrete girders, supporting the full-depth pre-stressed deck panels. The panels were post-tensioned along the spans during construction. SDR was tasked with instrumentation plan development, installation, and load testing of the bridge in order to study behavior of the bridge at various stages of construction, as well as during service life.

A series of nine load tests were conducted to validate operation of the installed Structural Health Monitoring (SHM) system. Measurement of the bridge’s response to these loading tests created a benchmark for future evaluation of the bridge’s long-term performance.

WESTBANK EXPRESSWAY INSTRUMENTATION AND LOAD TESTING

The Westbank Expressway is a six-lane freeway extending from Westwood Drive in Marrero, Louisiana, to the Crescent City Connection Bridge across the Mississippi River in New Orleans, Louisiana. The primary purpose of the proposed ramp project is to complete the MacArthur Interchange and reduce the distance between successive westbound off-ramps and eastbound on-ramps by providing access ramps from the service roads to the elevated expressway. Along this six-mile portion of the expressway, damage has been documented to the existing structure, especially the inverted-T pier caps, in both the eastbound and westbound directions.

SDR was selected by LADOTD to perform the following tasks:

Perform detailed investigation of reinforced concrete caps and girder seat bearings.
Perform finite element analysis and stress analysis of the inverted T caps.
Perform instrumentation and load testing of representative caps.
Present repair recommendations.

In the load testing stage of this project, one expansion end and one fixed end of representative caps were chosen for monitoring. During the load testing process, linear variable differential transformers (LVDTs) and strain gauges were used to measure the crack opening and strains in the proximity of damaged and undamaged areas under truck loads.

As a result of load testing and numerical simulations, it was concluded that exterior girder hanger bars were deficient; therefore, strengthening recommendations using CFRP wraps, bars or post-tensioning bars were presented. It was also concluded that cracks in the inverted T caps did not affect their structural performance, but they should be sealed for durability purposes.

BAYOU PIERRE BRIDGE LOAD TESTING

The Bayou Pierre Bridge is located between Desoto and Red River Parishes in Louisiana. The bridge owner requested that SDR perform independent analysis and testing of the existing structure to examine the possibility of transporting a special permit vehicle, called the dragline, across the bridge. Unloaded, this vehicle weighs around 7,100 kips. When loaded, the vehicle weighs around 10,000 kips. Each span of this bridge consists of 10 prestressed concrete girders; the substructure consists of a concrete cap and steel piles.

Analysis was performed in accordance with AASHTO LRFD using SmartBridge Suite software. A refined 3D Finite Element Analysis was also performed. Analysis results concluded that the piles would experience settlement during the vehicle passing. The results also indicated the possibility of permanent cracking of the prestressed concrete girders; therefore, it was decided to continuously monitor the bridge during the passing of the dragline vehicle and to reduce the weight of the vehicle compared to the originally proposed weight.

For the load testing stage of the project, strain gauges were placed along the girders and piles to measure the stresses and forces in critical members. Linear variable differential transformers (LVDTs) were used to measure the settlement of the structure. A series of preliminary bridge tests were performed to determine the overall bridge response and the possibility of settlement; results were used to calibrate the FE model.

During passing of the Dragline, no damages that compromise the structural integrity of the bridge were witnessed. SDR performed a follow-up inspection which showed only minor spalling and damage, verifying the good structural health of the bridge after the passage of the dragline.

MARTA CN915 BRIDGE

The MARTA CN915 light rail bridge experienced cracking and various structural deficiencies. This project consisted of preparing bridge strengthening plans using carbon fiber polymer (CFRP) and installing a 128-channel remote monitoring data acquisition system. The instrumentation consisted of strain and temperature sensors and was distributed over four spans that formed one of the bridge’s continuous units. A full 3-D finite element analysis was performed prior to proceeding with the instrumentation plan. SDR also conducted onsite load testing and has been remotely monitoring the bridge behavior since 2008.

MACARTHUR INTERCHANGE US-90 BUSINESS PHASE I

Full evaluation of the completed bridge widening was carried out under a task for peer review, where several constructability and detailing issues were discovered. SDR performed a full 3-D finite element analysis of the existing bridge, including the inverted-T piers, as well as a bridge load test. After further evaluation it was determined that the widening plans were deficient and re-design was required. SDR was tasked with the design and production of final plans of all superstructure elements, including the prestressed U girders and LG girders, deck, inverted-T caps and columns, and all complex columns with unbalanced loads. In addition, due to the structural complexity of the existing inverted-T piers, SDR performed a special analysis to evaluate and determine the cut lines for accommodating the widening. The evaluation of existing cut lines was performed and new alignment was developed.