STRUCTURAL EVALUATION OF SLAB 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 a 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 due to load testing capturing actual behavior of the structure (load distribution) and accounting for strength-enhancing factors that were not included in design.
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 to perform the structural evaluation though load testing of the slab spans with the aim of removing current posting.
Test results, along with FEA, reveal that due to support conditions of the slab, partial fixed end moments developed, causing significant reduction in mid-span moment as compared to moment calculated assuming simple-beam action. Furthermore, the slab behaves in a 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 an increased load rating factor, from 0.75 to 1.22.

WILLIAMS ROAD/SW 66 BRIDGE OVER I-75

The Williams Road/SW 66 Street bridge over I-75 in Ocala, Florida was built in 1989. The bridge consists of four (4) spans with a total bridge length of 272.5 ft. The superstructure comprises four (4) AASHTO Type III precast prestressed concrete beams. The bridge was impacted by an over-height truck, causing damage to exterior and interior beams. Damage to both beams was in the form of partial loss of concrete section in the bottom flanges and webs with exposed prestressing strands, but with no rupture of prestressing strands. During inspection it was also found that the exterior beam had old repair at the right end of the beam and exhibited signs of distress, e.g. cracking and delamination.
Repair of the beams included restoring the concrete section of the bottom flanges and webs.  Also, externally-bonded CFRP was applied to confine the restored section and provide redundancy to the shear strength. The repair method allowed I-75 to remain open during construction.

LA-1 OVER I-49

LA-1 over I-49 bridge was built in 1989. The as-built bridge consists of four continuous, steel plate girder spans with a total bridge length of 403 ft. and 45 degrees skew.
SDR performed thorough document review, hands-on inspection, surveying, and detailed analysis. A topographic survey revealed that both abutments are experiencing excessive settlement and lateral movement, resulting in transverse shear and uplift forces on the bearings at both abutments; increased reactions at intermediate bents causing over-stress and excessive deformation of bearing pads; redistribution of loads to internal supports, exerting more force on the foundations of internal bents; and additional negative moment, causing high tensile stresses and significant cracking of the deck.

SDR presented three alternatives to rehabilitate the bridge. The selected alternative consisted of adding two end spans of 100 ft. each to reduce embankment height and utilizing wraparound Mechanically Stabilized Earth (MSE) walls. In addition, SDR provided construction support.

LA-66 BIG BAYOU SARA BRIDGE

Big Bayou Sara Bridge is a historic bridge (built in 1949), carrying LA-66 over Big Bayou Sara in the West Feliciana Parish, Louisiana. The bridge main spans are comprised of five 100 ft. steel pony trusses, while the approach spans are comprised of five 40 ft. steel I-beam spans with a total bridge length of 700 ft.
Services provided by SDR included in-depth inspection of the superstructure and substructure of the bridge; development of 3-D Finite Element models to determine internal forces; evaluation of the existing structure to determine deficient elements; design of a rehabilitation system for the superstructure and substructure; development of preliminary and final plans for construction; design of a two-lane detour temporary steel bridge to be constructed on the north side of the existing bridge to maintain traffic during rehabilitation work on the existing bridge; development of cost estimation and schedule; and construction support.

MONITORING & TESTING OF US-80 BAYOU LAFOURCHE BRIDGE

Bayou Lafourche Bridge is located on US-80 over Bayou Lafourche Diversion Canal. The bridge comprises seven equal spans, each 80 ft. in length, with a total bridge length of 560 ft. The two end spans on each side and the three intermediate spans are continuous. The bridge cross-section consists of six precast prestressed concrete (PPC) girders supporting full-depth precast concrete deck panels. The precast deck panels are post-tensioned along the span during construction to close the gaps between the panels and to achieve composite action between the deck and girders after pouring the shear pockets. This accelerated bridge construction (ABC) technique was implemented for the first time in Louisiana; therefore, a monitoring and instrumentation program was carried out to study the behavior of the bridge at different stages of construction as well as during service life. After completion and before opening to traffic, nine load tests were conducted using calibrated trucks. The load tests are a benchmark for future monitoring to evaluate the long-term performance of the bridge.
Instrumentation used included vibrating wire strain gages attached to the rebar of the deck and girders; vibrating wire strand meters clamped to prestressing strands of the girders; weldable strain gages attached to connection plates; load cells; and hydraulic jacks.
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US-90 MACARTHUR DRIVE INTERCHANGE PHASE I

Phase I of MacArthur Drive Interchange is to provide ramp connections between the westbound direction of US 90 Business (Westbank Expressway) and the westbound frontage road near Peters Road and Harvey Tunnel. The Westbank Expressway was constructed as a four lane, divided, limited access highway in the late 1950’s along with the original Greater New Orleans Mississippi River Bridge and the Harvey Tunnel.

SDR’s first task was to carry out a bridge load test coupled with detailed 3-D finite element (FE) modeling of the existing bridge including the inverted-T piers. The results from the complex non-linear FE modeling and the load testing were used to determine the bridge sufficiency. The bridge was found to be sound and a recommendation to proceed with the bridge widening project was made to LADOTD. SDR was also tasked with the design and final plans production of all complex superstructure elements consisting of precast prestressed U-girders and LG-girders, inverted-T cap beams, and all complex columns with unbalanced loads. In addition, due to the structural complexity of the existing inverted-T piers, special analysis was required to evaluate and determine the cut lines for accommodating the widening which, was also performed by SDR.


SDR staff knowledge and experience was essential in proposing new design that is simple and cost effective while maintaining all aesthetic aspects of the existing bridge.

US-11 LAKE PONTCHARTRAIN BRIDGE

The US 11 Lake Pontchartrain Bridge is an historic bridge (built in 1928) carrying US 11 over Lake Pontchartrain, Louisiana. The bridge consists of 700 reinforced concrete spans and two steel movable spans, for a total length of 24,922 ft. Inspection of the bridge revealed wide cracks, and section loss on the bridge from deck to bent columns. SDR performed hands-on inspection, damage assessment, and designed rehabilitation of all structural components of the concrete superstructure and substructure. Major tasks included hands-on inspection of the fixed concrete bridge spans and substructure in order to determine the level and type of the structural deficiencies designated in the structural inventory reports; perform chloride ion penetration analysis to determine the diffusion coefficient and expected service life of the bridge; load rating the bridge, using traditional analysis, as well as refined analysis through linear and non-linear 3-D finite element models; conduct diagnostic load tests using strain gauges and loaded trucks; compile an evaluation report with repair recommendations; design bridge rehabilitation including detailed plans, special provisions, and construction cost estimation; and providing construction support.

DR. HATEM SELIEM PRESENTED AT THE AMERICAN ASSOCIATION OF PORT AUTHORITIES

Increasing the live load-carrying capacity of structures is crucial for extending the life span of infrastructure, due to commonly available heavier moving live loads as compared to the originally designed live load. Utilizing a combination of advanced modeling techniques, instrumentation, monitoring, and testing provides an accurate assessment of the structural load capacity. This capacity can be further enhanced through strengthening with Fiber Reinforced Polymers (FRP) to achieve the desired increase in load capacity and meet operational load demand. Along with enhancement of load capacity, FRPs provide the desired durability to extend the structure’s life span.
Dr. Seliem’s presentation at the American Association of Port Authorities, Engineering Facilities Seminar offers an overview of the strengthening technique along with examples of field applications where FRP’s have been successfully used for repair and strengthening of infrastructures.

DR. ZHIYONG “JOHN” LIANG PRESENTED ABOUT BRIDGE PRESERVATION AT SEBPP

Dr. Zhiyong (John) Liang, Vice President of SDR Engineering Consultants, Inc. during his presentation at the 2019 Southeast Bridge Preservation Partnership (SEBPP) held in Baton Rouge, Louisiana on April 16 to 18, 2019.
Dr. Liang presented SDR’s work on the use of Cathodic Protection as part of the rehabilitation of US-11 Lake Pontchartrain Bridge.