This article presents the recorded and modeled strong-motion response of a long (1.35 km) bridge located in Wellington, New Zealand during multiple sequential earthquakes. These were some of the ...first recordings of this kind for a New Zealand highway bridge and add to the limited database of bridge superstructure strong-motion responses recorded worldwide. The bridge experienced little damage during the earthquakes; however, analysis of the recorded responses showed the fundamental period of the bridge varied by up to 15% across these events, highlighting the system softening that can develop without any significant structural damage. Numerical models of a single bridge pier using a p-y spring foundation modeling approach were able to represent the changes in the recorded bridge pier response across the events based on multiple response metrics, suggesting that system softening was primarily due to nonlinear soil response and concrete cracking. A sensitivity analysis showed that concrete strength and the characteristics of the upper soil layers had the largest influence on the model response. Given the presence of several strong-motion stations in close vicinity to the bridge, the sensitivity to ground-motion input was also investigated. This was shown to have a more significant influence on the modeled response than the other modeling uncertainties evaluated here, with the variability in estimated deformations highlighting the difficulties involved in the back analysis of the response of structures.
Structures utilizing precast concrete walls have wide usage around the world, yet previous earthquakes have revealed the seismic performance of those walls is often deficient. These deficiencies can ...result in shear sliding at the wall base or brittle shear failure of the wall. These failure modes have been shown to be suppressed through the use of diagonal reinforcement in cast-in-situ walls, however, the tolerances and reinforcement geometry make the use of diagonal reinforcement in precast walls very difficult to achieve. In this paper, as an alternative to traditional diagonal reinforcement, X-shaped steel plate bracing was adopted in precast concrete walls and connected with welded joints. The experimental tests of four walls are presented, all of which incorporated the bracing and used either a cast-in-situ or bolted steel connection. The influence of the foundation connection and X-shaped steel plate bracing on the seismic performance of walls with different shear span ratios is described. The X-shaped steel plate bracing was found to effectively control shear sliding, with a greater decrease in shear sliding for walls with a lower shear span ratio. The bracing improved the peak strength of the walls, but the improvement varied with the angle of the bracing. The precast concrete walls with X-shaped steel plate bracing performed similar flexural failure modes to the reinforced concrete walls with a low shear span ratio but formed a plastic zone at the mid-height of the wall panel for the precast wall with a shear span ratio of 2.282. Numerical models developed for the precast concrete walls were able to estimate the force-displacement relationships.
Due to the extrusion manufacturing process, hollow‐core units in New Zealand do not have transverse shear reinforcement. The prestressing strands will not be fully developed near the ends of the ...hollow‐core units, which significantly affects the shear capacity and makes them prone to transverse and web cracking under deformation demands. In addition, initial end slip of the strands caused during cutting of the units in the production process may exacerbate this effect. This vulnerability of hollow‐core slabs was remarked during the 2016 Kaikōura earthquake, where an estimated 22% of the damaged buildings presented transverse cracking to hollow‐core units, sometimes accompanied by evident web cracking. The observed damaged, produced by earthquake‐imposed deformations, highlighted the urgency to advance the understanding of the behavior of hollow‐core floors. Subsequently, an experimental testing program was initiated to investigate the properties of extruded concrete and the shear strength of hollow‐core units under different shear span‐to‐depth or aspect ratios. The 200 mm deep specimens were loaded well beyond the peak shear force to study the postpeak behavior of the hollow‐core units. Additionally, the present study evaluates the effect of initial end slip of the prestressing strands on the pre and postpeak capacity of the units. The results obtained are compared against the formulations provided by commonly used design standards such as the New Zealand concrete standard NZS3101:2006, the ACI 318‐19, as well as the fib Model Code 2010 and the BS EN 1168:2005.
Corrosion of reinforcing steel bars (rebar) is one of the primary factors leading to the performance degradation of reinforced concrete (RC) structures. It is essential to take into consideration the ...deteriorating effects of corrosion when it comes to assessing the performance of existing RC structures. However, due to the uncertainties and randomness associated with the degree and distribution of corrosion, accurately assessing the residual deformation capacity of corroded rebar is a significant challenge. This paper presents a comprehensive theoretical model for the prediction of the residual deformation capacity of corroded rebar. Taking into account the mechanical characteristics of the steel material, three classes of non-uniform corrosion in rebar are firstly defined on a quantitative basis to characterize the deformation distribution patterns under tension. Based on the concept of deformation accumulation, a simplified theoretical model is proposed for evaluating the residual deformation capacity of corroded rebar, incorporating both the non-uniformity of corrosion and the sample (or gauge) length; thus, a length scale is built into the nominal strain measure to accommodate the use of different sample or gauge lengths. Numerical tensile tests on 500 randomly generated samples of rebar with varying corrosion levels are conducted, and the parameters of the theoretical model for the three corrosion classes are determined based on a regression analysis of the tensile test results. Comparisons with actual experimental results and existing degradation models demonstrate that the proposed theoretical model provides a more accurate estimation for the deformation capacity of corroded rebar. The model offers a reliable reference for accurately assessing the tensile performance of corroded rebar in subsequent engineering applications.
•A new prediction model is developed for the ultimate strain of corroded steel rebars•Classification criteria are introduced for three patterns of non-uniform corroded rebars•Theoretical formulation is established for the ultimate strain in three different classes•Probabilistic-based numerical test is used to generate data for determining model parameters•Experimental data is collected from literature, and the new prediction model is validated
AbstractThe durability of older reinforced concrete structures is significantly affected by corrosion of the steel reinforcing bars, and assessing the seismic capacity of such corroded RC structures ...is a challenging task. A simplified mechanics-based assessment procedure was developed to account for the effect of corrosion on the residual strength and displacement capacity of corroded RC members. The procedure was verified against a large database of experimental results from the available literature. A case study of a severely corroded RC building in New Zealand, constructed in 1928, was assessed using the proposed methodology. Although no change in failure mechanism was found, the overall displacement capacity of the building was 25% lower than the assessed uncorroded condition. Long-term corrosion effects were investigated for the case study building assuming no remediation of corroded reinforcing bars. It was found that the displacement capacity would be significantly reduced via the formation of story collapse at less than 1% drift after 30 years of continued corrosion deterioration if no remediation was made.
Pitting corrosion impairs the mechanical behaviour of reinforcing steel bars (rebar), reducing both the tensile strength and deformation capacity of the rebar. Existing models for predicting ultimate ...tensile deformation of pitted rebars are generally associated with fixed gauge lengths, failing to consider strain distributions within/outside the pit region. This study aims to establish a unified description of the ultimate tensile deformation capacity for pitted rebars under variable gauge lengths. Uniaxial tensile tests were conducted on 30 rebar specimens with simulated pitting corrosion damages by machined defects/notches. Parameters investigated included pit shape, cross-sectional area loss level, pit length, rebar diameter, and circumferential pit distribution. To determine the precise distribution of strain along the length of the rebar specimen, the Digital Image Correlation (DIC) technique was employed to provide a comprehensive visualization of the local strain distribution within and outside the pit region. The ultimate stress and strain distribution patterns were analysed under different parameter conditions. A predictive model was proposed for ultimate deformation capacity of rebar with pitting corrosion under a variable gauge length.
•Tensile tests conducted on 30 rebar specimens with simulated pitting corrosion.•DIC technique used to visualize local strain distribution.•Effects of pit morphology on corroded bar were thoroughly analysed.•Predictive model proposed for ultimate deformation capacity of pitted rebars.
Summarized in this article are the major findings from a detailed damage investigation of an instrumented ductile reinforced concrete moment frame building subjected to a design-level earthquake. The ...building sustained widespread damage during the 2016 M-7.8 Kaikoura earthquake and was subsequently demolished. Prior to demolition, the structural system was extensively surveyed to document the severity and distribution of the damage sustained in the reinforced concrete frames and the flooring system. Furthermore, the building response during the earthquake was reconstructed from the acceleration records obtained from instruments installed throughout the building. The site seismic demands were also obtained from a local free-field instrument. The data collected from this damage investigation provide a high-quality dataset that is valuable to researchers investigating different parameters related to the seismic performance of reinforced concrete moment frame buildings. The dataset is published and publicly available on DesignSafe-CI (project PRJ-3444); https://www.designsafe-ci.org/data/browser/public/designsafe.storage.published/PRJ-3444v2. The data collection methodology is described, and a roadmap for navigating the dataset is presented to support future use of the archived dataset.
Precast concrete wall panels are a common structural system, particularly in low-rise industrial and commercial buildings. In past earthquakes the connections between precast concrete panels and ...other structural members have been found to perform poorly. Fourteen panel-to-foundation assemblages were tested to investigate the out-of-plane performance of common connection detailing. These connection details included both dowel starter bars formed from conventional reinforcement, such as hooked bars, as well as starter bars connected to the panel via the use of cast-in threaded inserts. Variations in panel strength and connection strength were incorporated across the range of tested assemblages, and both cyclic and monotonic loading conditions were considered within the test program. It was found that conventional starter bars performed well because the presence of the hook returns of the starter bars within the joint region elevated the joint strength. Conversely it was found that panels having threaded inserts performed unsatisfactorily due to flexural cracking that propagated vertically behind the insert heads, leading to separation of the panel from the starter bars. It was determined that because the panels were close to the minimum reinforcement ratio, that the drift demands were very sensitive to the assumed cracking moment of the panel. Due to the brittle behaviour of the panel-to-foundation connection, it is advised that existing panels utilizing this connection be limited to less than 2% drift in the out-of-plane direction in order to avoid joint failure.
The different failure modes of composite floors subjected to in-plane shear forces have been determined by a number of researchers using pseudo-static testing. However, all previous experimental ...tests subjected the floors to a combination of shear and moment and did not represent the boundary conditions applying at the diaphragm interfaces with the seismic resisting system. This paper proposes a new experimental test setup in which the slabs being tested are subjected to near pure shear at the slab to supporting beam interface. Using the new experimental test setup, three composite floor slabs have been tested. In the first floor slab, the deck rib orientation is parallel to the supporting beam. For the second and third floor slab configurations, the deck rib orientation is perpendicular to the supporting beam. The second floor slab uses the standard end anchorage details adopted in New Zealand, involving a solid rib of concrete surrounding the shear studs along the secondary beam. The third floor slab uses the standard end anchorage detail adopted in Europe, in which the decking continues over the secondary beam and the shear studs are welded through the decking.
It was found that all three slabs had similar strength and stiffness, albeit with different failure modes. The first slab exhibited the most brittle behaviour, whereas the second specimen exhibited a smoother post-peak behaviour and was the most ductile among these three details. A comparison between the test results and existing design equations has been made and a new equation is developed.
•The in-plane shear behaviour of composite slabs was investigated through monotonic tests.•Although they had different end anchorage details, they showed similar strength and stiffness.•The contribution of steel deck and shear studs in shear strength of composite diaphragm was negligible.•The reduction of stiffness in all specimens up to peak load was slight.
AbstractThere has been little full-scale physical experimentation to support the findings of numerous computational studies regarding the contribution of various substructure components to overall ...bridge-foundation system behavior. In response to this lack of experimental data, a field testing program was undertaken to investigate the in situ dynamic characteristics of a 27-m-long, three-span, precast-concrete bridge. Forced vibration testing and system identification were used to characterize the dominant modal behavior of the bridge-foundation system in each loading direction, leading to identification of the likely force-transfer mechanisms between the structure and the substructure components. It was determined that both the transverse and longitudinal responses of the bridge were dominated by the abutment stiffness, with the passive resistance of the buried settlement slab contributing significantly to the transverse response and the backfill passive resistance dominating the longitudinal response.
