Three-dimensional Frame Model Research Articles

Seismic response control effects for reinforced-concrete buildings incorporating a passive variable friction device

The seismic response behavior and control effects of reinforced concrete (RC) structures incorporating a variable friction damper were numerically investigated in this study. The damper considered was a passive displacement-dependent variable friction device (VFD), whose sliding force decreases as the device displacement increases. A nonlinear response simulation was carried out using a single-degree-of-freedom system model under various input motions. The results showed that the VFD was effective for controlling the response of the RC structure, not only for reducing the displacement but also for mitigating the increase in the story shear force and acceleration. Also, the nonlinear earthquake response of a three-dimensional frame model representing a historic RC temple building retrofitted with VFDs was assessed. The results showed that the VFDs clearly mitigated the peak story shear of the device-installed story, compared with a passive conventional friction device (CFD). The VFD significantly reduced the peak story drift of the device-installed story compared with the uncontrolled case. Moreover, the peak story drift at the base story for the VFD was decreased compared to the CFD. The VFD contributes to enhancing the aseismic performance of RC superstructures while suppressing the stress increase in the foundation. • Assessment of the response control effects of RC structures with a variable friction device (VFD). • Sliding force of the VFD decreases as the device displacement increases. • Numerical nonlinear responses of SDOF and 3D frame models representing RC structures. • The VFD can mitigate the peak story shear force compared to a conventional friction device. • The VFD can reduce the peak story drift compared with the uncontrolled case.

Research on Construction Land Use Benefit and the Coupling Coordination Relationship Based on a Three-Dimensional Frame Model—A Case Study in the Lanzhou-Xining Urban Agglomeration

Coordinating the social, economic, and eco-environmental benefits of construction land use has become the key to the high-quality development of Lanzhou-Xining urban agglomerations (LXUA). Therefore, based on the coupling coordination connotation and interaction mechanism of construction land use benefit (CLUB), we measured the CLUB level and the coupling coordination degree (CCD) between its principal elements in LXUA from 2005 to 2018. Results showed that: (1) The construction land development intensity (CLDI) in the LXUA is generally low, and spatially presents a dual-core structure with Lanzhou and Xining urban areas as the core. (2) The comprehensive construction land use benefit has increased over time, but the overall level is not high. The spatial differentiation is obvious, and the core cities (Lanzhou and Xining) are significantly higher than other cities. (3) The regional differences in the subsystem benefit of construction land use are obvious. The social benefit and economic benefit showed a “convex” shape distribution pattern of “high in the middle and low in the east and west wings”, and regional differences of economic benefit vary greatly. The eco-environmental benefit was relatively high, showed a “concave” shape evolution in the east–west direction. (4) In addition, the CCD of the CLUB were still at a medium–low level. The higher the administrative level of the city, the better the economic foundation, and the higher or better the CCD of the social, economic, and eco-environmental benefits. (5) The CCD is inseparable from the influence of the three benefits of construction land use. Therefore, different regions should form their own targeted development paths to promote the coordinated and orderly development of LXUA.

Analysis of structural masonry buildings taking into account the construction sequence loads and soil-structure interaction

abstract: The present study assesses conventionally used design standards, analyzing the effects caused by the construction loads, that is, a gradual increase in load and stiffness during construction, and soil-structure interaction (SSI), with soil represented by linear springs, in a structural masonry building over a support structure of reinforced concrete. The equivalent frame model, developed by Nascimento Neto, was used to simulate the support structure and the first masonry floor, and a specific three-dimensional frame model to simulate the other floors. Four analysis models were applied to assess stress distribution at the base of the walls, and the stresses and displacements of the support structure. The results show that introducing SSI and the construction loads causes relief or the possible need to reinforce elements designed in Ultimate Limit State (ULS) and Serviceability Limit State (SLS), as well as uniform settlement.

SEISMIC EVALUATION AND RETROFIT ON AN EXISTING HOSPITAL BUILDING

The nonlinear pushover analysis was used to evaluate an existing 8-storey reinforced concrete framed hospital building under seismic force and presented in this manuscript. The ‘Guru Teg Bahadur Hospital' is one of the important hospitals at Delhi-India, it was selected for this research. The three-dimensional frame model was used to model the building with a fixed base. The beams and columns were modeled by using three-dimension line frame elements with the centre lines joined at nodes. Diagonal strut elements were used to model the brick masonry infills. The slabs were considered as rigid diaphragms. The plastic hinge rotation capacities as per Federal Emergency Management Agency 356 (FEMA 356) with Performance Levels were adopted in this study, considering the axial force-moment and shear force-moment interactions. The nonlinear pushover analysis of the selected building was done with infills and it was observed that the infills (due to their small number in the considered building) do not make any appreciable effect on the performance level, except their failure at an early stage. The Capacity Spectrum Method (CSM) and Displacement Coefficient Method (DCM) were used to estimate the performance point of the building. The values of various coefficients as per Federal Emergency Management Agency 440 (FEMA 440) were adopted. The DCM was observed to give slightly higher target displacements, as compared to CSM. It was observed in the nonlinear pushover analysis that the unreinforced masonry (URM) infills collapse before the performance point of the building for the Maximum Considered Earthquake (MCE). As the intervention inside the functioning hospital is extremely difficult, it was explored whether it is possible to safeguard the infills by stiffening the building by providing external buttresses. Two cases of retrofitting schemes with 1.2m wide and 3m wide buttresses in transverse direction were used and analysed. It was found that this is not a practicable approach, as the infills collapse even with 3m wide buttresses.

An Analytical Approach for the Flexural Robustness of Seismically Designed RC Building Frames Against Progressive Collapse

Quantitative and parametric investigations of the flexural robustness of seismically designed reinforced concrete (RC) building frames under column loss were conducted in this study. A robustness index expressed as the product of the seismic coefficient and the resistance ratio was proposed for the evaluation. Under column-loss conditions, the building frame may not sustain the effective seismic weight using the flexural mechanism as the robustness index is smaller than one. Analytical formulae of the robustness index for the three-dimensional frame model were derived using the energy method and plastic analysis technique. Seven moment-resisting RC building frames with different structural parameters were designed. Nonlinear static analyses were performed to investigate the effects of the span length, number of stories, and seismic coefficient on the robustness index. The results indicated that among these parameters, the span length was the most critical factor. The robustness index decreased with an increase in the span length. For the five-story building frames, it decreased to smaller than 1.0 when the span length increased from 4 to 6 m or larger. Nevertheless, the robustness index was approximately directly proportional to the seismic coefficient and number of stories. It was doubled as the seismic coefficient or number of stories increased from 0.1 to 0.2 or five to ten, respectively. Numerical verification confirmed that the proposed analytical formulae can provide conservative robustness evaluation for seismically designed RC building frames.

Implementation of potential flow hydrodynamics to time-domain analysis of flexible platforms of floating offshore wind turbines

In the design of supporting platforms of floating offshore wind turbines, global response analysis is essential to predict the response under various loads from wave, wind, moorings and the wind turbines. However, the literature of the global analysis of floating offshore wind turbines combining flexible modelling of the supporting platform and the potential flow theory for hydrodynamic evaluation is limited. In this study, the framework implementing the potential flow hydrodynamics to the time-domain analysis of the three-dimensional frame model was developed using modal decomposition for the hydrodynamic evaluations. The method utilized the assumption that the number of modes can be limited to those with larger contributions, which can lead to the reduction of the calculation cost. A spar-type floating offshore wind turbine was modelled to verify the implementation of the developed formulations. Results showed that the implemented method is effective in predicting the dynamic motion and deformation of floating offshore wind turbines under combined wind and wave loads. For the cases of the irregular waves, the results obtained with potential flow hydrodynamics showed smaller responses than the results from the Morison’s equation in the natural frequencies of rigid body motion, which might be attributed to the steady and low frequency external forces introduced in the Morison’s equation by considering the instantaneous position of the floater.

Implementation of real-time seismic diagnostic system on emergency management center buildings: system introduction and operational status on municipal government office buildings

In preparation for a major earthquake in the Nankai Trough, the authors plan to introduce a real-time seismic diagnostic system for emergency management center building clusters in the Aichi prefecture eastern region in Japan. The system involves installing seismometers (three-axis accelerometers) in the buildings and storing observation records in a cloud-based internet system (the Cloud) in real time. Immediately after an earthquake, a simple diagnosis of the building’s residual seismic performance is performed using a lumped-mass model and emergency management officials are notified of the results by email. Also, a detailed analysis of the damaged condition using a three-dimensional frame model is performed for several hours after the event to try to assess the specific building parts that are damaged. This paper describes the proposed system and then presents the results of setting up the system and conducting trial operations in municipal government office buildings as a test case prior to actual system implementation.

Earthquake Response Analysis of the Historic Reinforced Concrete Temple Otaniha Hakodate Betsuin after Seismic Retrofitting with Friction Dampers

ABSTRACT The main hall of Otaniha Hakodate Betsuin completed in 1915 is a historic reinforced concrete temple located in Hakodate, Japan. This temple was designated as an Important Cultural Property of Japan in 2007. Seismic retrofitting using supplemental vibration control devices, such as friction dampers, may be an effective approach for upgrading the aseismic performance of the temple. In the present study, nonlinear response analysis using two numerical three-dimensional frame models subjected to strong input motions was conducted to predict the aseismic performance of the temple without retrofitting and after retrofitting with friction dampers. The results indicate that the installation of the friction dampers would enhance the aseismic performance of the temple by improving the energy dissipation, stiffness, and seismic capacity of the temple. However, the increase in the seismic capacity of the main story achieved by incorporating the dampers would increase the response acceleration at the roof level.

Transverse assessment of a concrete box girder bridge

This paper looks at the beneficial effects of geometric arching from haunches, web continuity and compressive membrane action in the design and assessment of box girder top slabs. The paper initially reviews tests relevant to arching action in box girders and then analyses recent tests on box girder slab strips. Finally, using the assessment of an existing box girder bridge as an example, a series of computer models is developed to illustrate a method for transverse analysis of a box girder top slab in which some of these arching effects can be utilised. For the analysis of tests and the assessment example, a three-dimensional frame model that considers the in-plane strength enhancement of the restrained slab is used. This simplified approach was verified by finite-element modelling and the results show good agreement. The analysis methods including arching action significantly reduce the required amount of reinforcement for the deck slab. The paper concludes that arching action from geometrical arching of haunches and frame action are significant and must be considered for any accurate analysis at both serviceability and ultimate limit states. It is also concluded that compressive membrane action may occur and can be used in the design and assessment of box girder structures within certain geometric parameters.

Identification of jack-up spudcan fixity by an output-only substructural strategy

In jack-up design and site-specific assessment, the inclusion of spudcan fixity is an important but challenging task from the viewpoint of accurately quantifying the soil stiffness for each individual spudcan footing. To this end, a time domain output-only identification strategy is proposed in this paper to identify spudcan fixity parameters from only acceleration signals based on an improved genetic algorithm method. The numerical integration algorithm for the dynamic equation is modified to eliminate the need of measuring input forces, and a substructuring strategy is necessarily incorporated to overcome the otherwise computationally difficult (if not impossible) task. As an illustration example, a real jack-up is studied as a three-dimensional frame model with parameters under different foundational and environmental conditions. The numerical study demonstrates the power of the proposed strategy in accurate and efficient identification of jack-up spudcan fixity using limited response measurements.

Pushover Response of a Braced Frame with Suspended Zipper Struts

This paper presents the results from an experimental pushover test on a one-third-scale model of a special inverted-V-braced steel frame with zipper struts. Zipper elements are vertical elements added at the intersections of the braces above the first floor and designed to carry upward the unbalanced loads resulting from buckling of the braces. As far as the writers know, this is the first test on such a configuration that has been suggested as an alternate to conventional braced frames in the American Institute of Steel Construction seismic specification for many years. The model was pushed to a target roof drift ratio of +3.58%, which was achieved without strength degradation and followed a trilinear backbone curve. The load was then reversed until the bottom story brace in tension fractured at a drift of -0.78%. After this fracture, the frame still carried about 37% of the maximum base shear. The zipper elements demonstrated their ability to activate buckling in all stories except the top one, redistributing the loads in the structure and minimizing strength losses. Two-dimensional and one three-dimensional frame models were analyzed and found to reproduce satisfactorily the experimental results up to the beginning of tearing in the tension brace.

DYNAMIC TORSIONAL BEHAVIOR OF A BUILDING SUPPORTED BY UNSYMMETRICALLY ARRAYED PILES

In this study, centrifuge model tests have been carried out to evaluate the torsional behavior of pile-supported buildings with the eccentric distance between the center of gravity of the superstructure and the center of rigidity of the piles. Three models were considered; a 9-pile model without eccentricity, an 8-pile model which lacks a corner pile, and a 7-pile model which lacks two corner piles. It was found from the test that the maximum response of the torsional angle of a foundation increases in accordance with the eccentricity which is defined as the same method as the superstructure. The analysis was then carried out to simulate the result of the 7-pile model. In the analysis, a three-dimensional frame model was used, and soil around the piles was modeled as two directional horizontal axial elements and shear springs. A comparison between experimental and analytical results shows a possibility that this numerical model is capable of considering the dynamic torsional behavior of buildings supported by unsymmetrically arrayed piles.

Damage detection in framed buildings

The transformation matrix method for damage detection in structural elements of frame buildings, expressed as the loss of stiffness, is proposed and evaluated. The method, which allows the locating and assessing of the damage magnitude of structural elements by considering the contribution of each of them to the overall performance of the structure, is applicable to two- and three-dimensional building frames of several storeys and bays with one or several damaged elements. Effects of uncertainties in the experimental measurements of the dynamic characteristics and in the precision of the numerical representation of the structure on the method proposed are evaluated. A three-dimensional frame model with different simulated damage states and a reinforced concrete plane frame model damaged using an earthquake record as excitation are studied. Results show the good agreement between the estimated damage computed with the proposed method and the true value of damage.Key words: damage detection, transformation matrix, structural damage, damage assessment.

Damage detection in framed buildings

The transformation matrix method for damage detection in structural elements of frame buildings, expressed as the loss of stiffness, is proposed and evaluated. The method, which allows the locating and assessing of the damage magnitude of structural elements by considering the contribution of each of them to the overall performance of the structure, is applicable to two- and three-dimensional building frames of several storeys and bays with one or several damaged elements. Effects of uncertainties in the experimental measurements of the dynamic characteristics and in the precision of the numerical representation of the structure on the method proposed are evaluated. A three-dimensional frame model with different simulated damage states and a reinforced concrete plane frame model damaged using an earthquake record as excitation are studied. Results show the good agreement between the estimated damage computed with the proposed method and the true value of damage.Key words: damage detection, transformation matrix, structural damage, damage assessment.

Impact response of thin-walled frame structures

This paper describes a finite-element method which was developed to predict the impact response of three-dimensional thin-walled frame structures. The softening effect of the load-deformation characteristics for thin-walled beams under combined axial compression, bending and torsional loads during impact is simulated by making use of a nonlinear Maxwell model. The large deformation of a structure is calculated by using updated nodal coordinates and internal forces, and the flexibility matrix for a curved beam element. Crash tests against a flat barrier were made on three-dimensional frame models. Comparisons between the calculated and experimental force-time relations and the deformed shape of the frame are discussed.

Design of Transverse-Plane Bulkheads in Tankers

A program system, INDETS, for computer-aided design of tanker structures has been developed. The system, which is the result of a joint effort of the Norwegian Institute of Technology, Trondheim, and the Aker Group, Oslo, is considered an effective tool for practical design. A design module of INDETS for tanker transverse-plane bulkheads is presented. The girder system is analyzed by a three-dimensional frame model including the surrounding structure as substructures. Two optimization methods, the Stress Ratio Technique and the Sequential Unconstrained Minimization Technique, are applied. A number of parametric variations on topology have been performed, and the depth and breadth have been varied to derive curves for estimating the weight of bulkheads at the preliminary design stage. As a conclusion, a simple-formula is presented.