Papers by Keyword: Seismic

Abstract: Recently, the frequency of earthquakes has been increasing worldwide. As a result, steel reinforced with seismic performance that can satisfy the social needs to strengthen the existing seismic performance of existing infrastructure facilities and new buildings has become important. In general, to secure the yield strength of reinforcing bars and to reduce the production cost, reinforcing bars are produced by rolling the surface through a facility such as a Tempcore. In Korea, most of them have adopted the Tempcore process to ensure the mechanical requirements of the product. However, the use of a small amount of alloying elements and the application of Tempcore have limitations in producing reinforcing bars that require seismic performance. In recent years, remarkable progress has been made in the production and application of high strength rebars. Microalloying and fine-grain strengthening are the most effective methods in developing high strength rebars. That is, the precipitation of V (C, N) is promoted by the addition of V to improve the strength by precipitation strengthening of V-carbonitride. However, in V-microalloyed reinforcing bars, it was confirmed that the required strength did not increase proportional to the amount of V added. In this study, the effects of vanadium and other alloying elements on the mechanical properties and yield ratio of steel bars were investigated by tensile test results and microstructural evaluation.

Abstract: Partially restrained beam-column connections can be used in the gravity load system of building structures to develop moment frame action to enhance collapse prevention for low-ductility steel lateral systems. The benefit from such reserve lateral strength and stiffness is illustrated for a low-rise building with steel braced frames designed in accordance with Canadian provisions for seismic force resisting systems of the Conventional Construction category. Preliminary results from a comprehensive cyclic test program recently completed on beam-to-column joints with bolted double web angle acting with top and seat angles are presented. The test program included 23 full-scale beam-to-column sub-assemblages subjected to combined gravity shear forces and cyclic rotational demands. Experimental observations on the deformation patterns and failure modes are presented together with representative hysteretic moment-rotation responses of bolted double web angles without and with top and seat angles.

Abstract: The essence of real-time hybrid simulation (RTHS) is its ability to combine the benefits ofphysical testing with those of computational simulations. Therefore, an understanding of the real-timecomputational issues and challenges is important, especially for RTHS of large systems, in advancingthe state of the art. To this end, RTHS of a 40-story (plus 4 basement stories) tall building havingnonlinear energy dissipation devices for mitigation of multiple natural hazards, including earthquakeand wind events, were conducted at the NHERI Lehigh Experimental Facility. An efficient implementationprocedure of the recently proposed explicit modified KR-a (MKR-a) method was developedfor performing the RTHS. This paper discusses this implementation procedure and the real-time computationalissues and challenges with regard to this implementation procedure. Some results from theRTHS involving earthquake loading are presented to highlight the need for and application of RTHSin performance based design of tall buildings under earthquake hazard.

Abstract: The current design approach for moment connections in many seismic specifications worldwide focuses on providing energy dissipation to achieve a collapse prevention objective. Most specifications only provide guidance for the design of beam-column connections in orthogonal configurations. However, it is not uncommon that for architectural reasons beams be required to frame into columns at an angle, either with respect to the horizontal (sloped connections) or with respect to a vertical plane (skewed connections), for the design of which little guidance is available. This paper presents a numerical study focusing on Bolted Flange Plate connections in non-orthogonal configurations. The response of these connections was compared to extant experimental results, using orthogonal configurations as a baseline. Investigating the connections response in terms of moment-rotation capacity, stress distributions, plastic strain demands, and plastic hinge locations, some recommendations for the design of non-orthogonal Bolted Flange Plate connections are presented. Secondarily, a study of the influence of specific details on the response of the connections was performed, resulting in practical detailing recommendations.

Abstract: Hot-rolled products such as beams are usually subject to rotary straightening as a last step in the manufacturing process. This operation may change the properties of the plastically deformed area by strain hardening. The affected regions of the beam are referred to as the “k-area”, as shown in Figure 1. Strain hardening reduces the ductility and notch toughness of the steel and can potentially lead to cracking in the k-area when welding is carried out in restrained conditions e.g. addition of stiffeners by welding. The phenomenon was reported for wide flange beams in the US literature in the 1990s. Welding limitations and increased inspection requirements in these areas were introduced to AISC and AWS D1.8 codes [1]. Similar requirements can be found in New Zealand Standard NZS 3404.1 [2]. However, it is unclear if steel products used in New Zealand are affected by this phenomenon. A series of welding and performance tests were carried out at HERA using hot rolled products UB610, UC310, UB310 and UC200 of material grade 300S0 to AS/NZS 3679.1 [3]. The material is commonly used in New Zealand for seismic construction. Welded test specimens were subject to a range of testing, including mechanical and cold cracking susceptibility tests. Test setup and results are reported in the paper. The authors present recommendations for future standard developments.

Abstract: Considering the effects of strain rate, the nonlinear dynamic response of two reinforced concrete(RC)structuresisstudied under seismic excitationsin this paper. Firstly, based on the model in a shaking table test, a three-dimensional finite element model of RC frame-shear wall structural model subjected to both horizontal and vertical component seismic excitations is established. The structural model is a three-story RC frame-shear wall structure, which consists of RC slabs, RC columns and transverse spandrel beams.Afringeframe is infilled by a RCshear wall.Then, According to the practice engineering, a multi-story RC frame structure is also established. Finally, the dynamic response of the structures is investigated using nonlinear seismic analytical method considering the effects of strain rate. These results may provide a reference for seismic design of RC structure.

Abstract: The dynamic behavior of the prefabricated and cast in situ concrete shear wall structures subjected to seismic loading is investigated by finite element method. This paper adopted a prefabricated concrete shear wall in a practical engineering. The Precise finite element models of prefabricated and cast in situ concrete shear wall were established respectively by ABAQUS. The damaged plasticity model of concrete and kinematic hardening model of reinforcing steel were used. The top displacement, top acceleration, story drift ratio and base shear forceof prefabricated and cast in situ concrete shear wall under different seismic excitation were compared and analyzed. The earthquake resistant behaviorsof the two kinds of structuresare analyzed and compared. Results show that the performances of PC structure were equal to the cast-in-situ ones.

Abstract: Fragility curves for typical multi-span simply supported concrete box girder bridges in eastern China are presented. A set of bridge samples, of which five uncertain parameters are considered, is established using the Latin hypercube sampling. Nonlinear time history analyses are conducted to capture the structural response quantities. Probabilistic seismic demand models are formulated by quadratic regression analysis for the capacity/demand ratios. Fragility curves of bridge components are developed and the fragility of bridge system is evaluated using the first-order bound method. The results show that the columns and expansion bearings among bridge members are more fragile under earthquake excitation, and the bridge system is more fragile than any bridge component. The typical bridges have more than 50% probability when subjected to PGAs of 0.46, 0.58, 0.82, and 1.0g for four damage states, respectively. The fragility curves can be used for retrofit prioritization for this type of bridges.

Abstract: In the areas prone to natural disasters, ability of lifeline systems from catastrophic damages is one of the most important challenges in civil engineering. One of the most important structures is elevated water tanks. Most of the damages observed to these structures under seismic events are due to the improper design and wrong selection of supporting system. This paper investigates the suitability of interlocking system for staging of an elevated water tank of higher capacity. As a preliminary study the performance of concrete interlock panelled tower under static condition is analyzed by considering the standard earth gravity under full and empty conditions. The study concludes that the new system can perform in a similar way as that of the conventional system.

Abstract: FRP confinement of sub-standard columns with low quality concrete, light transverse reinforcement and improper reinforcement detailing is widely accepted as an efficient retrofitting strategy. This paper introduces an improved method using carbon fiber reinforced polymers (CFRP) and external steel ties for seismic retrofitting of full-scale rectangular reinforced concrete columns loaded in their weak directions. Three cantilever columns with a cross-sectional aspect ratio of two (600 mm x 300 mm) are tested under constant axial load and reversed cyclic lateral loads. The columns are representative of existing substandard members with characteristics such as low concrete quality, low transverse reinforcement ratio, plain bars and high axial load level. The test results indicate that columns retrofitted with FRP jacketing and external steel ties significantly benefit from the applied retrofit scheme particularly in terms of ductility and energy dissipation. Additionally, the experimental results are compared with the performance predictions of seismic assessment and design documents.