Rehabilitating and Repairing the Buildings and Bridges of Americas: Hemispheric Workshop on Future Directions

Ductility of reinforced concrete flexural members depends on the amount and detailing of ordinary reinforcing steel bars. The addition of carbon Fiber Reinforced Polymer (CFRP) composites, which is another form of tension reinforcement, will affect the ductility of concrete flexural members strengthened with CFRP sheets. Several researchers in Japan, Europe, and the United States have investigated the use of CFRP for increasing the flexural strength of concrete flexural members. However, the flexural ductility with respect to the amount of existing ordinary steel bars has not been investigated in depth. In addition, delamination of CFRP sheets dominates the ultimate mode of failure of flexural members strengthened with CFRP sheets, which limits the ductility of strengthened members. End anchors could be used to prevent the debonding of CFRP sheets and enhancing the flexural ductility. This paper presents the results of an experimental investigation of seven full-scale reinforced concrete beams strengthened with CFRP composite sheets. The main variables are the amount of the existing reinforcing steel bars in the beams, and the use of CFRP anchorage. The amount (size and type) of the longitudinal CFRP sheets was maintained constant. Test results have shown that strengthened beams with lower amount of existing ordinary steel bars have lower flexural ductility. Test results have also shown that CFRP anchorage could significantly increase the flexural ductility of CFRP strengthened beams. Such important findings should be reflected on the design equations of CFRP sheets required for strengthening existing reinforced concrete beams to ensure an acceptable level of flexural ductility.

This paper presents a detailed outline pertaining to the rehabilitation of three timber railroad bridges located along the South Branch Valley Railroad (SBVR), in Moorefield, West Virginia. All three timber bridges were at least 50 years old, and acquired major renovations for adaptation to modern railroad traffic applications, i.e. 20 percent increase in load carrying capacity to accommodate the weight of a 315 kip locomotive. The refurbishment consisted primarily of piles, pile caps, and bridge stringers that were in an advanced state of decay. These sections were refurbished either in-situ or by temporary removal and prompt on-site renovation. The renovation consisted of: 1) Complete removal of loose/decayed material; 2) Existing cavity replenishment with consistent bulk adhesive; 3) Proper application of selected primer; 4) Suitable wrapping of resin soaked fabric on piles, pile caps, and bridge stringers; and 5) Reinsertion of original bridge stringers after refurbishment with glass composite wraps. Load testing results from a portion of these initial bridges revealed that renovations accounted for relative stiffness values that are approximately double in comparison to the original substrates. The above renovation technique is non-intrusive, structurally sound, and economical proficient. Currently, an on-going monitoring program of the renovated bridge structures should provide us with a wealth of technical information, and establish the durability of the proposed renovation methodology.

There is no more effective tool for transferring repair and retrofit technologies than a proof-of-concept test on a large model structure. Such tests can addresses concerns related to scale effects, 3D interaction (floor effects and force redistribution), and impact of non-structural elements and secondary (gravity) structural systems that are typically associated with small scale models and/or component tests. As part of an on-going project sponsored by the Mid-America Earthquake Center, a large two-story, full-scale unreinforced masonry building will be tested at Georgia Tech in the summer of 2001. The primary intent of the test is to investigate the effectiveness of two types of repair techniques that have been proposed for URM walls: FRP sheets and vertical prestressing. There will be multiple test conducted (i.e, initial cracking, first "yield" (i.e., rocking or sliding of some piers), initial repairs, damage into non-linear range, additional repair /strengthening, and tests to ultimate. The focus of the studies is to assess the effects of local repairs on overall building performance, i.e., to study the impact of a few, carefully selected repairs on the system response. In this paper the authors will report on: 1) the results of the extensive analytical studies conducted to date as part of the planning of this test, including expected failure sequences for the system, 2) the difficulties encountered in modeling even this relatively simple structure under dynamic loads, 3) assessment of current FEMA 273 and Eurocode provisions for evaluating the strength of existing and repaired walls, 4) studies on concrete specimens to assess the effects of environmental factors of the durability and reliability of FRP repairs, 5) comparisons with a companion, ½-scale test to be run on a shaking table at the US Army Corp of Engineers Civil Engineering Research Laboratory (CERL), and 6) preliminary studies conducted at the CERL laboratory on different FRP retrofit technologies, and at the University of Illinois on vertical prestressing. It is expected that all of these issues will be touched upon for the presentation, while the first three will constitute the bulk of the written contribution. As the testing is still in the planning phase and as URM construction is of great importance in Latin America, interaction at this workshop could offer an opportunity to both test some innovative ideas from Latin American researchers and to involve some of them directly in the testing and processing of the results.

This work presents the experimental evaluation of the mechanical and structural properties of a bridge deck developed at Georgia Institute of Technology made of Fiber-Reinforced Polymers (FRP), specifically vinyl ester resin reinforced with E-Glass fibers. Two reinforcement schemes are used: 2-D non-crimp stitched fabrics (NCF), and 3-D triaxial braided preform (3-D braid). The panels are constructed by binding together with epoxy adhesive beams of triangular section with two flat plates to form the top and bottom surfaces. The material is first characterized at the coupon-size specimen level, where the physical and mechanical properties are determined. The structural properties of the beams with triangular section are determined by flexural tests where an arrangement of three potentiometers are used to measure simultaneously vertical and horizontal deflections, and rotation, including the use of a gravity load simulator. Finally, the flexural properties of the decks are determined by subjecting five-cell assemblage prototypes to single patch load. Pultruded triangular beams reinforced with the 3-D braid are recommended for the final prototype because it eliminates some of the problem encountered with the lay-up version. The bridge deck specimens resisted approximately 5.5 times the design load, from which it was concluded that the design is dominated by flexibility limit state. It is recommended to develop design methodologies that accounts for the uncertainties associated with the material property, manufacturing, and dimensional variabilities.

The shear resistance of seven reinforced concrete beams were tested, as part of a M.Sc. thesis, using concrete strength between 53.8 and 70.3 MPa, with GFRP (glass fiber reinforced plastics) bars as flexure reinforcement, with and without steel shear reinforcement, a/d equal to 2.5. The beams were 150 x 300 x 3000 mm, with variable longitudinal flexural and transversal ratio of reinforcement. The ratio of longitudinal flexural reinforcement varies between 1.60 and 3.26%, while the shear ratio of reinforcement varies between 0.096 e 0.150%. The results indicate that the two modifications proposed by Michaluk (1998), of multiplying all the concrete contribution (1) or only the flexural ratio of reinforcement in the concrete contribution (2), respectively, by the ratio of the elasticity modulus of the GFRP and the steel (E_gfrp/E_s), do not present good results. This indicates that the concrete contribution in the shear resistance is not susceptible to the plain ratio of elasticity modulus. The results also show that deflections obtained at "service load", corresponding to the maximum deflection in service allowed by the codes, are in average 1.24 times bigger than the estimated for the cracked section, indicating that the inertia adopted are bigger than the real one in this case.

Fiber optic sensors applied to existing bridges can be used to extend service or ease load restrictions by collecting data on fatigue cycles, overloads, and crack propagation. Fiber optic sensors can be used for several bridge monitoring purposes: traffic monitoring, WIM for load spectra, deflections, vibration signatures and acoustic emissions crack propagation. Most of these can be done simultaneously with the proper system design and calibration. There are several types of fiber optics, each based on a different property of the light waves traveling down a fiber. The two types that are commercially available for measuring strains parallel to the fiber are Fabry-Perot, which measures interference fringes, and Bragg grating, which measures frequency. The sensors can also be incorporated into accelerometers, gyroscopes and other types of measuring devices. They have several advantages over conventional electronic sensors including compactness, freedom from drift and electromagnetic interference, and ruggedness. Multiple Bragg grating type sensors can be photo-imprinted along the same fiber, making it feasible to install large scale networks of 1000 sensors or more. Such a fine grid provides sufficient data for advanced nonlinear dynamics analysis based on chaos theory to detect cracks and other types of damage.

In the last five years, a major effort in Canada in the field of health monitoring of structures using fibre optic sensors (FOSs) and wireless remote monitoring technologies has been conducted through the ISIS (Intelligent Sensing for Innovative Structures) Canada, a Network of Centres of Excellence of Canada. In this paper, recent activities and major advances by ISIS Canada in the area of health monitoring of civil engineering structures will be reviewed. The paper will provide the state-of-the-art technologies developed by ISIS researchers in the areas of FOSs and wireless remote monitoring. Various field applications of these technologies will be discussed. Sample data and their retrieval system will be highlighted. A bridge project in Alberta will be used to illustrate the versatility and potential of the technologies in the assessment and monitoring of structures. Finally, current and future efforts undertaken by ISIS Canada in the field of structural health monitoring will be discussed.

Since the adoption of the National Bridge Inspection Standards, State Departments of Transportation have invested significant resources in the inspection and evaluation of highway bridges. Inspections have relied largely on visual inspection of bridge to assess the condition of bridges, and few nondestructive evaluation (NDE) methods have been widely adopted. Given the large numbers of deteriorating bridges, there is a need to develop new and better tools for the condition assessment of bridges. This paper presents some of the new technologies being developed by the FHWA for the NDE of highway bridges. The FHWA NDE Validation Center is described, and a brief overview of a recent study on the reliability of normal bridge inspection practices is provided. Several recent efforts to develop unique tools for the condition assessment and health monitoring of in-service bridges are described.

This paper presents the findings of an experimental study on the use of Infrared Thermography for nondestructive evaluation of subsurface delaminations in Fiber Reinforced Polymer (FRP) composite bridge decks and concrete columns wrapped with FRP jackets. Composite bridge deck specimens were constructed in the laboratory with varying subsurface delamination conditions such as sizes, thicknesses and filler materials. These simulated delaminations were placed between the 3/8 inches thick wearing surface and the top of the FRP deck. The laboratory specimens were tested using an infrared imaging system. The infrared images from the delaminated specimens were compared with solid (undamaged) specimens to study the effect of subsurface delaminations on the infrared images under controlled laboratory conditions. In addition, field tests were conducted using infrared thermography on the FRP composite decks of two bridges (Wickwire Run and Laurel Lick) located in West Virginia. The field tests were used to detect subsurface delaminations and study the effect of environmental parameters on the infrared images. As an additional example, infrared testing was conducted to evaluate FRP wrapping and detect debonding between the FRP wraps and concrete columns in the Pond Creek Bridge in West Virginia. This study shows that the infrared thermography technique can be used effectively for rapid evaluation of subsurface condition of FRP composite bridge decks and wrapped columns. The study also shows how the environmental conditions (e.g., shadow, oil spill, and angle of reflection of solar rays) can affect the output infrared images.

Civil structures, including buildings and bridges, have not been given high priority for application of advanced nondestructive evaluation (NDE) techniques as compared with aircraft and aerospace structures. Although in recent years there has been an increase in nondestructive techniques for construction materials such as concrete and wood, the funding for these techniques is miniscule compared with that spent on advanced materials for military applications. In fact visual inspection once every two years is the primary technique used for routine inspection of bridges, and buildings have been given even less attention. Conventional nondestructive testing (NDT) is only used as an adjunct to visual inspection and very few advanced nondestructive evaluation (NDE) techniques are used at all. This paper will present an overview of the current nondestructive methods used for inspection of civil structures. Examples will be given of developments over the recent past which have resulted in improvements in nondestructive inspection of civil structures and techniques. Also to be discussed are those methods used in other applications and those emerging from research laboratories, which afford the potential to greatly improve NDE techniques for inspecting civil structures.

A general diagnosis is presented on the seismic vulnerability of bridges of the main public road network in Colombia based on approximate evaluations and inspection of bridges. For the bridges identified as critical, a methodology is proposed to carry a detailed evaluation of seismic vulnerability considering simultaneously the live load capacity of the structure and the residual useful life of the bridge. The methodology includes the compilation of information (structural, geotechnical and foundation details), the evaluation of the properties of materials of the main structure, the evaluation of the behavior and characteristics of the bridge such as deflections and internal forces on elements under known loads, and registration and interpretation of environmental and forced vibrations. Based on the information the evaluation of seismic vulnerability of the bridge is established through capacity/demand ratios for the different elements and possible types of failure of the structure. General criteria are established to define intervention alternatives. Two case studies are presented of the proposed methodology for bridges of the public road network of Colombia.

An innovative approach to concrete slab-on-girder bridge deck design in which all internal concrete reinforcement can be removed is discussed. The removal of conventional steel rebar eliminates deterioration associated with corrosion of the reinforcement and thereby improves the durability and longevity of the deck. The innovative design has been implemented in six field projects in Canada and is a feasible solution for both new construction and rehabilitated structures. Three of the field rehabilitation projects are presented, two bridge structures and one marine structure, in which the innovative system was utilized. The improved understanding of bridge deck behaviour can also be used to produce durable rehabilitation schemes in designs where conventional internal reinforcement layouts are desired.

The United States of America Federal Highway Association (FHWA) estimates the average annual investment to retire all backlog/accruing bridge deficiencies for years 1992–2011 as $8.2 billion. To encourage the efficient use of available funds, FHWA recommends considering rehabilitation alternatives before replacing a structure. The goal of bridge management is to assess the structures most critically in need of repair/strengthening, decide the appropriate retrofit, and control cost. This paper discusses several technology transfer opportunities such as PONTIS as a bridge management system and PACES for estimating repair/rebuild alternatives. In determining which structures are most critical for repair/strengthening, PONTIS provides a database of bridge assessment. PONTIS, a network level management system, does not include a project level evaluation that assesses various costs associated with alternative repair procedures. This paper highlights the design and conceptual basis of a cost benefit model for bridges. This model addresses the process of constructing the repair, provides resulting costs, builds on the Parametric Cost Engineering System that contains worldwide area cost data and construction methods, and contributes new and fundamental interdisciplinary systems-based knowledge applicable to bridge infrastructure systems. This model design: provides economically smart repair/strengthening options; provides a fundamentally new process to document the decision processes; provides an audit trail on repair alternatives; and provides the basis for documenting lessons learned. The authors believe the model reported herein is valuable for international bridge managers.

The paper is concencerned with the evaluation, strengthening and follow-up of two case studies of multispan prestressed concrete bridges in Argentina. The two case studies, and the ensueing repair works, were prompted by different circumstances: one of them, by the catastrophic collapse of one of twelve identical 60 m span arches -tied by the presetressed concrete deck- after passage of a regular passenger bus, and the other one, consisting of fourteen simply supported spans of cast-in-place prestressed concrete girders, by systematic and excessive deformations and cracking of the longitudinal girders. Although both cases were built more than 30 years ago used for prestressing a postensioning system (Hoyer) no longer applied in Argentina, and were located in the same geographic region with similar mild environmental conditions (temperate weather, with rains concentrated on the summer months), the difference between their respective structural configurations led to very different critical limit states. The tied arch collapsed without warning just after a bus had passed over the bridge; the collapsed span was the last of the twelve spans the bus had passed. At the time of collapse no signs of damage or of abnormal structural behavior had been noticed. The experimental and modelling forensic study revealed that failure of the prestressed concrete tie beams near the arch abutments incorporated to the structure of the deck was the cause of collapse. The failure mechanism involved only partial redistribution of forces from the broken high stregnth steel tendons of the tie beams to the reinforced concrete deck slab before the onset of collapse. The tendon failure was found to have been caused by corrosion associated with the spilling of a water on the initial section of the tie beam by a drainage pipe of the water runoff of the bridge deck. Design of the external prestressing needed to restore the safety requirements of the eleven identical spans that remained in service was immediately undertaken, implemented and controlled by a follow up process of the prestressing force of the new external tendons. On the other hand, the simply supported beams reached a service limit state of excessive vertical deflections and cracking, that led to bridge owner to restrict the circulation over the bridge to a maximum of one truck in one of the two traffic lanes. The experimental and analytical evaluation that followed indicated the the load capacity of the bridge was not at stake, but that new external prestressing to compensate for the excessive losses of prestressing force was needed to improve durability. The paper presents in detail the various aspects of the structural evaluation performed, from dynamic load tests and material properties to the criteria for design of the external prestressing and control of performance after carrying out the repair work.

This paper presents an alternative means for reinforcing masonry structural systems in buildings located within seismically active regions. Masonry structural members are reinforced and/or confined with polymer grids, rather than conventional strengthening elements such as reinforced concrete (RC) or steel. Special qualities of the grid reinforcement promote ductile behavior of the masonry system and help realize its potential for high strength. The technical characteristics of the reinforcement and masonry components are described, after which rules are given for application to new, damaged and historical buildings. Laboratory test results validate the proposed reinforcing strategies for various structural systems, while the existing database supports various conceptual designs. The new reinforcing method is easily applied and economical.

The structural collapse of a 26-story apartment building is analyzed in this paper. The crushing of a concrete column in the first floor caused the collapse of part of the building, comprising 44 apartments from the first to the last floor. Laboratory tests of reinforcement samples and concrete cores extracted from remaining structural elements indicated that the strengths of the materials were in accordance with prescribed design values. In situ inspections revealed signs of faulty construction such as insufficient concrete cover and absence of cross-ties in the columns. The analysis of the structure showed that some columns had a low safety factor and high longitudinal reinforcement ratios, not complying with most codes of practice. The implications of such construction and design errors occurring simultaneously were analyzed in order to identify the most probable cause of the collapse. Questions related to the reasons why a structure under sustained loads could fail after years, in the absence of overloads and foundation settlement, are also addressed in the paper.

A pony truss span bridge of 110 feet long, built by the Bureau of Public Roads (BPR) in 1944, is analyzed and a rehabilitation process is designed in order to keep the bridge in service during the construction time. No fresh concrete could be used to rebuild the slab because the vibration due to transit load would avoid the concrete hardening process, then a post-tensioned slab was designed in order to assembly each lane by parts and bond all the parts by a compression force. It was necessary to add stringers to the floor structure in order to support the parts of one lane before the post-tensioning process was accomplished. The analysis of stress was performed using actual transit loads and the post-tension compression forces. A longitudinal compression stress was generated in order to avoid tension stresses during transit and earthquake loading. The trusses were transformed in statically indeterminate trusses to reduce deformation and reduce the vibration periods. Temperature stresses were generated in the trusses during temperature changes, however they were evaluated and considered as minor stresses. The number and amplitude of load and unload cycles in the old structure and in the repaired structure were added to confirm that fatigue is far to be attained.