Journal of Performance of Constructed Facilities

Pier columns, as primary bridge supports, are vulnerable to extreme loading demands resulting from fire, vehicle collisions, and blasts. The combined effects of these demands may cause significant strength reduction, extensive damage, and potentially collapse. Although the response of bridge columns subjected to independent or combined vehicle impact and air blast has been widely investigated, the cumulative effects of fire in conjunction with these dynamic loads have received limited attention. Consequently, this study presents a unique and advanced multistep finite-element modeling approach using LS-DYNA to simulate the response of isolated round reinforced concrete bridge columns subjected to fire prior to and after a vehicle collision and subsequent air blast. The developed modeling approach incorporates uncoupled implicit heat transfer analyses and explicit structural analyses and was validated against published fire, impact, and blast test results. A parametric study that investigated the effects of various column diameters and fire exposure scenarios on performance was completed, considering fire occurring before or after impact and blast. Column performance was assessed based on damage levels, residual load capacities, and lateral displacements. Study findings enhance the understanding of bridge column performance under this combination of hazards, provide insight into improving bridge resiliency, and could potentially have practical implications for the design and maintenance of bridge columns. Specifically, the study reveals that fire prior to impact and blast was a more critical load sequence for larger column diameters that could potentially remain in service in their final damage states while being repaired. Moreover, the study indicated that for the same fire duration and column diameters, residual capacities and displacements corresponding to half-surface-area exposure were slightly lower than those exposed to fire on the full surface area, a finding that could be beneficial in many practical applications where protective techniques and tools could be implemented.

Hybrid columns with partial structural steel-reinforced concrete (SRC) and reinforced concrete (RC) sections in the transfer stories of buildings are prone to premature shear failure due to sudden changes in load bearing and stiffness properties. An experimental program was undertaken in this study to investigate the influence of the length of embedment of structural steel in hybrid SRC-RC columns bending around strong and weak axes. Five large-scale specimens with varying lengths of embedded structural steel were tested under gradually increasing lateral cyclic displacements and constant axial load. The main parameters studied were the failure mechanism, hysteretic response, energy dissipation potential, and lateral stiffness of test specimens. Test results showed that all SRC-RC specimens, irrespective of the direction of lateral loading, had higher lateral strengths than the RC columns. However, specimens with the lower embedment of structural steel performed poorly due to shear-dominated failure. Test results also highlighted the detailing requirements for lateral ties in the zone where structural steel was not present to promote the flexural mode of failure. Numerical analysis based on finite element modeling was carried out to predict the strength and failure mechanism of SRC-RC columns. Based on the findings of this study, recommendations are suggested for the design and detailing of these columns for practical applications.

Abstract

This paper focuses on concrete degradation of hydraulic conveyance components of a hydropower project in Uganda that was commissioned in 2019. During a routine outage inspection in 2021, concrete damage was observed in the waterways. The engineering-procure-construct (EPC) contractor was notified to remedy the defects but they declined, claiming that it was normal erosion wear. In order to ascertain the root cause, avert a potential dispute, and apportion liability, a forensic investigation was conducted by the owner. Site inspections, water quality sampling and testing, and concrete core sampling and testing were carried out during the forensic investigation. The findings indicate that the Nile River water is highly aggressive, and the coupled soft water attack and hydraulic erosion-abrasion led to the premature concrete surface degradation. In order to enhance durability and long-term performance of the waterways, a protective surface coating has been recommended. The investigations have been very useful to avert costly and time-consuming disputes between the owner and the contractor because the cause and party responsible for the defects have been identified, and the contractor has agreed to take remedial action in accordance with the contract. The study will be useful for other planned hydropower projects along the Nile River and similar projects globally.

Practical Applications

The paper reveals the significance of forensic investigations at a hydropower infrastructure project to ascertain the durability of the civil engineering components of the facility, and in turn the overall performance of the infrastructure. The study undertakes a forensic investigation of concrete degradation within hydraulic conveyance components of a recently commissioned hydropower project in Uganda. The findings reveal practical insights for industry practitioners on the key design and construction considerations for hydropower plants or similar water conveyance systems. Key findings from the investigations, as well as durability recommendations for future project waterways, are shared for best industry practice, including adopting a comprehensive durability design and performance-based approach for key infrastructure such as hydropower plants.

Recent collapses of reinforced and prestressed concrete bridges have been attributed to corrosion and construction flaws, which are often belied by an outward appearance of robustness. The true nature of degradation being obscured, routine monitoring may fail to capture serious defects. Two simple analytical methods are presented herein for the prediction of corrosion damage evolution as a means of supplementing routine inspections. The first approach captures load redistribution between concrete and corroded reinforcement, based on the principles of compatibility and equilibrium. Corrosion is modeled by decreasing the effective reinforcement area and reducing the reinforcement strength and ductility according to models from the literature. The second method couples corrosion and fatigue damage by treating corrosion pits as fatigue initiation sites. It is shown that corrosion pits reach a critical point when their depth approaches one-half of the reinforcement diameter. Both schemes are implemented in a case study of the Morandi Bridge, inspections of which revealed the presence of internal corrosion damage and construction flaws upon its partial collapse in 2018.

The reliability of reinforced concrete bridge beams that are flexurally strengthened with externally bonded carbon fiber-reinforced polymer (CFRP) laminates according to current AASHTO design provisions was quantified. The flexural resistance model considers resistance loss due to the effect of bar corrosion, FRP rupture, and debonding. Random variables were used to characterize uncertainties in as-constructed initial beam geometry and material properties, as well as loads and loss of beam resistance due to steel, concrete, and CFRP system degradation. Bond strength loss was based on 19 years of actual in situ data. The effects of various critical parameters on reliability were quantified, including beam span, concrete strength, the modular ratio and unit area of CFRP, the extent of CFRP repair, and the dead/live-load ratio. It was found that a large inconsistency in reliability exists among CFRP-repaired beams designed according to AASHTO provisions, the primary cause of which is variability in debonding potential. The results demonstrate the importance of including a well-developed bond strength model in the design process. Recommendations are provided.

Thermally induced stresses can build up in rigid pavements without pressure relief joints. The pressure created becomes a problem for adjacent structures such as bridges. The pressure can cause the pavement to push on the bridge and close the bridge expansion joints. This sets the stage for additional distress if not repaired quickly. This paper presents a case study where excessive pavement pressure damaged a two-span conventional bridge spanning Interstate 35 in Moore, Oklahoma. The bridge was instrumented with vibrating wire sensors to gather information on the behavior of the bridge before and after the repairs. There is a dearth of sensor verified observations of excessive pavement pressure acting on conventional bridges. The sensor data provided in-depth information on the response of the distressed bridge before and after repairs to thermal loading. Prior to the repairs the approach pavement was pushing on the bridge deck and causing the abutment backwalls to tilt toward the bridge. Following the repairs, the approach pavement is no longer pushing on the bridge deck. However, the abutment backwall is now moving in response to thermal changes in the bridge deck, likely due to excessive friction between the deck and the abutment backwall. U-shaped shaped cracking and spalling, previously observed in integral abutment bridges, was observed at this conventional abutment bridge, and the mechanisms causing these cracks and spalling are discussed. Through this study it was found that placement of pavement pressure relief joints relative to the bridge is crucial for reducing the magnitude of stress acting on the bridge. It was also found that the pavement stress acting on a bridge deck can be estimated with vibrating wire strain gauges given a baseline strain response for the approach pavement.

Fire accidents often pose severe threats to the safety of steel bridges. This paper presents the numerical study of the Runyang Suspension Bridge (RSB) fire accident with an emphasis on its in-fire thermal effect on the hangers. This fire accident was caused by the collision of two heavy-goods vehicles (HGVs) on March 4, 2017, and lasted for 1.5 h. Based on the simulated temperature, the structural safety of four burned hangers during and after the fire accident was evaluated and compared. In general, the simulation results are consistent with the actual situation, and the evidence for the replacement of the hangers is sufficient. The influence of wind parameters and cooling actions on the hanger safety is also discussed. It is found that the wind parameters affect the directions and tilts of the flame, so that the highest temperature and the corresponding height are influenced accordingly. Also, the efficiency of the water-cooling method is influenced by the intervention time of fire engines. If water spraying is conducted within 30 min from fire initiation, the safety of the hangers during and after the fire could be improved, as compared with air cooling.

This paper discusses the development of ultrasonic stress measurement (USM) technology as a potential tool for structural heath monitoring and evaluation of buildings and bridges. The proposed approach utilizes acoustic birefringence to assess the total stress in steel members. Acoustic birefringence describes the difference in velocity between orthogonally polarized shear waves as a result of anisotropy in the material. This anisotropy comes from texture produced during the manufacturing process and stresses (i.e., strains) in the plate under loading. The relationship between the birefringence and stresses may be a viable method to evaluate the total stress in a steel member, which includes stresses produced from all applied loads, including both dead loads and live loads. This paper investigates steel wide-flange (W-flange) rolled sections under tension and bending. The results indicate that birefringence shows a strong linear correlation with strain. The variation in the in situ birefringence was found to be significant and varied between different locations on the same cross section. If the acoustic constants ($B_0$ and $m_1$) that relate the birefringence to the strain are known, laboratory tests showed that stress can be approximated to within $\pm 1.1\mathrm{ksi}$ ($\pm 7.6\mathrm{MPa}$) (2% of the material yield strength, $F_y$). If average values of constants across all laboratory testing were used, the error increased to $\pm 14.79\mathrm{ksi}$ ($\pm 102.0\mathrm{MPa}$) (28% $F_y$). These results indicate that ultrasonic stress measurement based on acoustic birefringence measurements may be a viable method for the evaluation of total stress in steel members but needs additional research to identify and mitigate the sources of variation in critical acoustic constants that affect the accuracy of the approach.