Journal of Structural Engineering

This paper presents the main results obtained from field tests carried out in four sites of three recently built elevated viaducts in Mexico City. The main objectives of the tests were to determine and assess the structural response of elements located at representative sections of the viaducts. Focus was given to the identification of main static and dynamic properties, the measurement of the lateral displacement of the column-footing assemblage under monotonically increasing loads, and the study of the soil-structure interaction of the assembly. The field tests ranged from ambient vibration measurements to applying horizontal and vertical loads to the structure by means of pulling cranes and both parked and moving vehicles. The tests were aimed not only at providing experimental evidence to support the general assumptions used by the design firm, and to make the proper adjustments if deemed necessary, but to contribute to the body of knowledge with respect to elevated viaducts built by means of precast posttensioned members.

In situ push-over experiments and analytical assessments were conducted in this study to investigate the seismic capacity of RC school buildings at the Guan-miao Elementary School in Tainan City, Taiwan. Both prototype and external steel-framing specimens were constructed and compared. Reinforcements with steel channels were adhered to the captive columns and their adjacent beams in the weak direction, to retrofit the school building through the creation of external steel-framing systems. The design and construction procedures of the beam-column connection are introduced, as well as detailed drawings of the column-base anchorage system, both of which are key to the effects of the proposed retrofitting method. The experimental results show that the steel-framing system can be firmly bonded to the retrofitted specimen, providing continuous stress transference from the beam-column joints to the steel channels. The failure mode of the retrofitted captive columns was shifted from shear failure, as seen with the prototype specimen, to flexural-shear failure, with the retrofitted one. Both the experimental and analytical results show the following: The maximum total base shear strength increases 2.11 times, the total enclosed area of the stored energy increases 2.20 times, and ductility capacity increases 1.31 times. The external steel-framing systems proposed in this work can thus effectively enhance the base shear strength and the ductility of the specimens.

This paper describes instrumentation and autonomous, Web-enabled remote monitoring of in-service structures to resolve concerns. Structures were subject to dynamic excitation from blasting, construction equipment, and passing trains. An integrated approach to sensing, data acquisition, communication, data aggregation, and display was developed and successfully applied to structures ranging from bridges to homes. Challenges encountered and best practices developed over many multiyear continuous remote monitoring deployments are discussed. Deployment of monitoring and communication hardware and software and development of robust, autonomous, data aggregation, dissemination, and interpretation strategies are emphasized. Three selected case studies provide context and demonstrate applications of field monitoring to real-world situations on in-service structures. Autonomously acquired data were used to allay fears of construction vibration-related damage to a historic building, possible loss of capacity of bridge columns under quasi-static and dynamic loads, and blast-induced cracking of residences.

This paper reports the results of full-scale inelastic cyclic static tests of all-steel dismountable buckling restrained braces (BRBs) applied to an existing damaged reinforced concrete (RC) building. The two concepts set as the design targets for the prototype BRBs were to minimize interference with the functions and aesthetics of the existing building and to use an all-steel dismountable solution to allow for inspection of the yielding core after earthquakes. Two masonry infill panels (typical in RC buildings) were used to hide the braces and satisfy the first objective. Specially designed steel built-up shapes with bolted connections were used to satisfy the second objective. The design criteria and procedure adopted for the retrofitting design are first described, and a description of the BRB specimens and the experimental results follows.

Over recent years there has been growing interest in building frequency analysis using ambient vibrations in the fields of structural engineering with application to earthquakes, health monitoring, or operative testing. The direct applications are (1) to define the modal characteristics of existing buildings for modeling their seismic response, (2) to monitor the long-term variations in their structural health, and (3) to detect and localize changes in the structure such as those produced by earthquake damage. Simultaneously, velocity measurements with laser remote sensing techniques have gained interest for several applications. For example, coherent lidar systems enable accurate measurement of the vibration velocity of remote targets. This allows operative modal analysis (OMA) of potentially damaged buildings, for their diagnosis from a safe distance after a seismic event. This paper compares the frequency analyses obtained using sensitive velocimeter sensors and coherent lidar sensors, applied to a number of existing reinforced concrete (RC) buildings. Ambient vibrations recorded by velocimeters are processed using the frequency domain decomposition method for defining building frequency and mode shape, while the laser remote sensing approach uses the coherent lidar method to measure velocity, frequency, and mode shape. The results of a real-scale trial on five buildings in Grenoble, France, are presented. The reliability of this technique for remote structural diagnosis is discussed and the modal parameters, as measured by lidar at a range of 200 m and by in situ velocimeters, are compared. The results from the two instruments were in good agreement, which leads us to conclude on the ability of the coherent lidar approach to assess the modal frequencies and mode shapes of existing buildings at long range and without any retroreflectors on the structure for structural and earthquake engineering purposes.

Horizontally curved, steel I-girder bridges can present unique challenges for engineers and contractors because the curved geometry can result in a complicated torsional response. The most complicated stages for predicting behavior of the girders usually occur during erection and construction when the loads and support conditions are the most unpredictable. Although laboratory experiments can provide valuable insight into the behavior, the high cost of the specimens often precludes meaningful experiments, whereas field monitoring of bridges during construction provides invaluable opportunities to understand the behavior and gather data for validating computational models. A horizontally curved, steel I-girder bridge was instrumented to monitor the bridge during erection and concrete deck placement. Stresses were monitored as girders were lifted into position, followed by measurements of vertical deflections, rotations, and stresses during the concrete deck placement. The stresses during the erection process were relatively low owing to the proper use of lifting and placing methods; however, high stresses can be induced after girders are placed when the cross frames are ratcheted into position. As expected, higher stresses, compared with the steel erection process, were recorded during the concrete deck placement. Nonetheless, the monitored bridge did not have stability problems because the bridge utilized a relatively stocky flange width-to-depth ratio. For bridges more susceptible to stability challenges, such as tightly curved bridges, highly skewed bridges, narrow bridges, bridges with odd span arrangement, or some combination of these attributes, it is recommended that the designer consider the implication of slender girders and explicitly design for the possibility of construction-related stability challenges. In addition, resulting from the limited availability of field measurements of horizontally curved girders throughout the construction process, the data represent a valuable resource researchers can use to validate computational models for conducting parametric investigations. This paper outlines the methods used during the field monitoring and summarizes the results from the field measurements.

Load tests on segmental bridges are uncommon in the literature given their relatively short history and comparatively smaller presence in the national bridge inventory. This paper presents results from two segmental concrete bridge field tests and compares them with common simplified longitudinal and transverse analysis procedures. These single-cell structures, built with balanced cantilever construction, represent two significantly different segmental concrete bridges. Designers frequently use a beamline model for longitudinal analysis. When compared with the load test results, this simple method produces conservative predictions of longitudinal behavior within 20%, which is also reflected in the literature. Conversely, little information exists in the literature on transverse bending analysis. When analyzing the localized transverse bending from concentrated wheel loads, designers commonly use an equivalent frame model. Most frequently, designers use influence surfaces to estimate the scaled loads to apply to these two-dimensional frame models. This simplified approach is shown to be conservative overall but cannot always predict bending sense and frequently overpredicts demand in excess of 100%.

A finite element (FE) model was calibrated using the data obtained from a full-scale test to failure of a 50 year old reinforced concrete (RC) railway bridge. The model was then used to assess the effectiveness of various strengthening schemes to increase the load-carrying capacity of the bridge. The bridge was a two-span continuous single-track trough bridge with a total length of 30 m, situated in Örnsköldsvik in northern Sweden. It was tested in situ as the bridge had been closed following the construction of a new section of the railway line. The test was planned to evaluate and calibrate models to predict the load-carrying capacity of the bridge and assess the strengthening schemes originally developed by the European research project called Sustainable bridges. The objective of the test was to investigate shear failure, rather than bending failure for which good calibrated models are already available. To that end, the bridge was strengthened in flexure before the test using near-surface mounted square section carbon fiber reinforced polymer (CFRP) bars. The ultimate failure mechanism turned into an interesting combination of bending, shear, torsion, and bond failures at an applied load of 11.7 MN (2,630 kips). A computer model was developed using specialized software to represent the response of the bridge during the test. It was calibrated using data from the test and was then used to calculate the actual capacity of the bridge in terms of train loading using the current Swedish load model which specifies a 330 kN (74 kips) axle weight. These calculations show that the unstrengthened bridge could sustain a load 4.7 times greater than the current load requirements (which is over six times the original design loading), whilst the strengthened bridge could sustain a load 6.5 times greater than currently required. Comparisons are also made with calculations using codes from Canada, Europe, and the United States.

It is well known that the in-plane behavior of flexible timber diaphragms has a large influence on the global earthquake response of unreinforced masonry (URM) buildings. The type and the activation of out-of-plane URM wall failure mechanisms are strictly related to diaphragm stiffness, which is a property that also governs the effectiveness of the diaphragm to distribute earthquake-induced loads between lateral load resisting wall elements. However, there is a lack of reported experimental campaigns pertaining to these issues, and in particular, few experimental data have been published on the in situ behavior of existing vintage flexible timber floor diaphragms such as single straight sheathed diaphragms that are typically encountered in New Zealand URM buildings. To address this paucity of available in situ test data, an experimental campaign was executed to investigate the as-built cyclic and dynamic behavior of full-scale vintage flexible timber floor diaphragms with the outcomes being presented herein. Two sections of a diaphragm located in a vintage two-story URM building, measuring $6.4\times 9.6\mathrm{m}$ and $4.6\times 9.6\mathrm{m}$, were subjected to a series of cyclic and snap back tests in the direction orthogonal to the floor joists. In order to reproduce a realistic inertial load distribution to the test specimens, an ad hoc loading system using wire ropes and steel pulleys was developed. The loading system was designed to be lightweight, versatile, and relocatable between test specimens. From the obtained test results, it was identified that the equivalent stiffness of existing timber diaphragms (in the direction orthogonal to the joists) is predicted with a certain degree of conservativeness using the most recent procedures currently available in literature, while reliance on the ASCE standard can lead to an overestimation of the floor diaphragm stiffness, even at small displacements. Due to the nonlinear behavior of the tested flexible timber diaphragms, the measured natural period proved to be highly dependent on the target displacement.

This paper describes the field testing of a decommissioned, skewed, steel I–girder bridge and the resulting behavior that was observed. To more thoroughly evaluate the behavior observed in the field testing, where a load 17 times the design load was applied, a finite element model of this bridge was created, which illustrates the behavior of this structure at an even greater load and in greater detail than could be achieved in the field. The field and finite element analysis (FEA) results for this bridge were compared with expectations based on current bridge specifications. These results show that there is significant reserve capacity in this common bridge configuration, relative to both current bridge design and rating specifications and the maximum load that could physically be applied to the structure. This is attributed to transverse redistribution of force enabling the strength of this bridge to far exceed the strength of the limiting girder, which is termed the system effect in this work. Conceptual formats that could be adopted to better capture this effect in future bridge specifications are also discussed.

This paper discusses a comprehensive investigation and retrofit for extensive fatigue cracks in the end connections of floor beams on a double-deck, cantilever-suspended steel truss bridge. The investigation involved three-dimensional (3D) finite-element analyses using global and local models, field measurement of strains and displacements due to live load and temperature, laboratory testing of steel samples for material properties and high-stress low-cycle fatigue characteristics, as well as development of an effective retrofit based on the analytical, experimental, and field testing results. It was concluded that the cracks were a result of distortion induced fatigue in the floor beam web due to interactive deformations of the global structural system under live load and temperature variations. The retrofit entailed removing the fatigue susceptible weld terminations and reinforcing local areas of the floor beam web for out-of-plane distortion. Construction of the fatigue retrofit was completed in July 2011. The repaired structure has performed satisfactorily since then.

Summary results from a series of field experiments at a test site in Greece are presented, involving an in situ instrumented bridge-pier model built on realistic foundation conditions, to study the dynamic behavior of structure-foundation-soil system. It was attempted to link the variation of its dynamic characteristics to certain changes in its structural system, including the development of structural damage. This measured response was next utilized to validate numerical tools capable of predicting influences arising from such structural changes as well as from soil–foundation interaction. This bridge-pier model was supported on soft soil deposits allowing the study of structure–foundation–soil interaction effects during low-to-medium intensity artificial excitations. The in situ experiments provided measurements that were used to verify fundamental analytical solutions for soil–structure interaction. They were also used to validate numerical simulations that were developed to predict the response of the studied structure and thus, back-evaluate modeling assumptions. The obtained accuracy of the numerical predictions must be partly attributed to sound knowledge of the mechanical properties of the pier model and of the soil, not necessarily the case in all practical applications. It is evident that more complex finite-element models can improve the quality of the prediction only in cases where their parameters can be defined equally well. A special study further focused on the radiation of the waves generated by the vibration of the bridge-pier model through the soil medium. It is deemed that this comprehensive experimental investigation of soil–structure interaction provides measurements of the system response and enhances our understanding of the physical phenomenon as a whole.

Structural identification continues to develop an expanding role within performance-based civil engineering by offering a means to construct high-fidelity analytical models of in-service structures calibrated to experimental field measurements. Although continued advances and case studies are needed to foster the transition of this technique from exploration to practice, potential applications are diverse and range from design validation, construction quality control, assessment of retrofit effectiveness, damage detection, and lifecycle assessment for long-term performance evaluation and structural health monitoring systems. Existing case studies have been primarily focused on large civil structures, specifically bridges, large buildings, and towers, and the limited studies exploring application to damaged structures have been primarily associated with seismic events or other conventional hazards. The current paper produces the first experimental application of structural identification to a component of a full-scale building structure with structural deterioration resulting from an internal blast load. Experimental modal analysis, nondestructive testing, and visual documentation of the structure was performed both prior to and after the internal blast, while a suite of blast overpressure transducers and shock accelerometers captured applied loads and structural response during the blast event. This paper presents an overview of the field testing and observed structural response followed by extensive treatment of the experimental characterization of structural damage in a masonry infill wall. Combined stochastic-deterministic system identification is applied to the acquired input-output data from the vibration testing to estimate the modal parameters of the infill wall for both the in-service state and in the postblast condition with damage characterized by interfacial cracking and permanent set deformation. Structural identification by global optimization of a modal parameter-based objective function using genetic algorithm is employed over two stages to produce calibrated finite-element models of the wall in the preblast and postblast conditions. Damage characterization is explored through changes in the structural properties of the calibrated models. Plausibility of the results are supported by observed cracking and spall documented in the experimental program and further reinforced through nonlinear applied element simulation of the response of the wall.