• Computers and Concrete
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• v.24 no.4
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• pp.379-397
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• 2019

Steel-concrete composite beams are widely employed in constructions and their performance at the serviceability stage is of concern among practitioners and design regulations. In this context, an accurate evaluation of long-term deflections via various rheological concrete models is needed. In this work, the performance and predict capability of some concrete creep and shrinkage models ACI, CEB, B3, FIB and GL2000 are ascertained, and compared by using statistical bias indicators. Ten steel-concrete composite beams with existing experimental and numerical results are then modeled for this purpose. The proposed modeling technique uses the finite element method, where the concrete slab and steel beam are modeled with shell finite elements. Concrete is considered as an aging viscoelastic material and cracking is treated with the common smeared approach. The results show that when the experimental ultimate shrinkage strain is used for calibration, all studied rheological models predict nearly similar deflections, which agree with the experimental data. In contrast, significance differences are encountered for some models, when none calibration is made prior to. A value between twenty and thirty times the cracking strain is recommended for the ultimate tensile strain in the tension stiffening model. Also, increasing the relative humidity and decreasing the ambient temperature can lead to a substantial reduction of slab cracking for beams under negative flexure. Finally, there is not a unique rheological model that clearly excels in all scenarios.

• Journal of the Korean Society for Railway
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• v.16 no.3
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• pp.175-182
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• 2013

Rolling noise is an important source of noise from railways; it is caused by wheel and rail vibrations induced by acoustic roughness at the wheel/rail contact. To reduce rolling noise, it is necessary to have a reliable prediction model that can be used to investigate the effects of various parameters related to the rolling noise. This paper deals with modeling rolling noise from wheel and rail vibrations. In this study, the track is modeled as a discretely supported beam by regarding concrete slab tracks, and the wheel vibration is simulated by using the finite element method. The vertical and lateral wheel/rail contact forces are modeled using the linearized Hertzian contact theory, and then the vibration responses of the wheel and rail are calculated to predict the radiated noise. To validate the proposed model, a field measurement was carried out for a test vehicle. It was found that the predicted result agrees well with the measured one, showing similar behavior in the frequency range between 200 and 4000 Hz where the rolling noise is prominent.

• International Journal of High-Rise Buildings
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• v.10 no.4
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• pp.265-283
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• 2021

To ensure that fire induced collapse of a building is prevented it is important to understand the sequence of events that can lead to this event. In this paper, the initiation of collapse mechanisms of generic a multi-storey steel frame subjected to vertical and horizontal travelling fires are analysed computationally by tracking the formation of plastic hinges in the frame and generation of fire induced loads. Both uniform and travelling fires are considered. In total 58 different cases are analysed using finite element software LS-DYNA. For the frame examined with a simple and generic structural arrangement and higher applied fire protection to the columns, the results indicate that collapse mechanisms for singe floor and multiple floor fires can be each split into two main groups. For single floor fires (taking place in the upper floors of the frame (Group S1)), collapse is initiated by the pull-in of external columns when heated beams in end bays go into catenary action. For single floor fires occurring on the lower floors(Group S2), failure is initiated (i.e. ultimate strain of the material is exceeded) after the local beam collapse. Failure in both groups for single floor fires is governed by the generation of high loads due to restrained thermal expansion and the loss of material strength. For multiple floor fires with a low number of fire floors (1 to 3) - Group M1, failure is dominated by the loss of material strength and collapse is mainly initiated by the pull-in of external columns. For the cases with a larger number of fire floors (5 to 10) - Group M2, failure is dominated by thermal expansion and collapse is mainly initiated by swaying of the frame to the side of fire origin. The results show that for the investigated frame initiation of collapse mechanisms are affected by the fire type, the number of fire floors, and the location of the fire floor. The findings of this study could be of use to designers of buildings when developing fire protection strategies for steel framed buildings where the potential for a multifloor fire exists.

• Advances in Computational Design
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• v.4 no.1
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• pp.53-72
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• 2019

Safety measures for tower cranes are extremely important among the seismic countermeasures at high-rise building construction sites. In particular, the collapse of a tower crane from a high position is a very serious catastrophe. An example of such an accident due to an earthquake is the case of the Taipei 101 Building (the author was the project director), which occurred on March 31, 2002. Failure of the bolted joints of the tower-crane mast was the direct cause of the collapse. Therefore, it is necessary to design for this eventuality and to take the necessary measures on construction sites. This can only be done by understanding the precise dynamic behavior of mast joints during an earthquake. Consequently, we created a new hybrid-element model (using beam, shell, and solid elements) that not only expressed the detailed behavior of the site joints of a tower-crane mast during an earthquake but also suppressed any increase in the total calculation time and revealed its behavior through computer simulations. Using the proposed structural model and simulation method, effective information for designing safe joints during earthquakes can be provided by considering workability (control of the bolt pretension axial force and other factors) and less construction cost. Notably, this analysis showed that the joint behavior of the initial pretension axial force of a bolt is considerably reduced after the axial force of the bolt exceeds the yield strength. A maximum decrease of 50% in the initial pretension axial force under the El Centro N-S Wave ($v_{max}=100cm/s$) was observed. Furthermore, this method can be applied to analyze the seismic responses of general temporary structures in construction sites.

• Structural Engineering and Mechanics
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• v.78 no.4
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• pp.485-496
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• 2021

So far analytical methods on collapse assessment of three-dimensional (3-D) steel frames have mainly focused on a single-column-removal scenario. However, the collapse of the Federal Building in the US due to car bomb explosion indicated that the loss of multiple columns may occur in the real structures, wherein the structures are more vulnerable to collapse. Meanwhile, the General Services Administration (GSA) in the US suggested that the removal of side columns of the structure has a great possibility to cause collapse. Therefore, this paper analytically deals with the robustness of 3-D steel frames in a two-side-column-removal (TSCR) scenario. Analytical method is first proposed to determine the collapse resistance of the frame during this column-removal procedure. The reliability of the analytical method is verified by the finite element results. Moreover, a design-based methodology is proposed to quickly assess the robustness of the frame due to a TSCR scenario. It is found the analytical method can reasonably predict the resistance-displacement relationship of the frame in the TSCR scenario, with an error generally less than 10%. The parametric numerical analyses suggest that the slab thickness mainly affects the plastic bearing capacity of the frame. The rebar diameter mainly affects the capacity of the frame at large displacement. However, the steel beam section height affects both the plastic and ultimate bearing capacity of the frame. A case study on a six-storey steel frame shows that the design-based methodology provides a conservative prediction on the robustness of the frame.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.2
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• pp.19-28
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• 2018

The progressive collapse resistance performance of a steel structure constructed using the moment frame with the WUF-B connection and the composite slabs was evaluated. GSA 2003 was adapted for the evaluation. Additionally the structural robustness and the sensitivity against the progressive collapse were analyzed. In the numerical analysis, a reduced model comprised of the beam and spring elements for WUF-B connection was adapted. The composite slab was modeled using the composite-shell element. Instead of the time-consuming dynamic analysis for the effect of the sudden column removal, the equivalent energy-based static analysis was effectively applied. The analysis results showed that the structure was the most vulnerable to in the case of the internal column removal, however it satisfied the chord rotation criterion of GSA 2003 due to the contribution of the composite slab which improved the stiffness of structure. In the robustness evaluation, the structural performance showed more than 2.5 times of the requirement according to GSA 2003, and the structural sensitivity analysis indicated the decrease of 33% of the initial structural performance.

• Ocean Systems Engineering
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• v.10 no.4
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• pp.399-414
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• 2020

A floating bridge is an innovative solution for deep-water and long-distance crossing. This paper presents a curved floating bridge's dynamic behaviors under the wind, wave, and current loads. Since the present curved bridge need not have mooring lines, its deep-water application can be more straightforward than conventional straight floating bridges with mooring lines. We solve the coupled interaction among the bridge girders, pontoons, and columns in the time-domain and to consider various load combinations to evaluate each force's contribution to overall dynamic responses. Discrete pontoons are uniformly spaced, and the pontoon's hydrodynamic coefficients and excitation forces are computed in the frequency domain by using the potential-theory-based 3D diffraction/radiation program. In the successive time-domain simulation, the Cummins equation is used for solving the pontoon's dynamics, and the bridge girders and columns are modeled by the beam theory and finite element formulation. Then, all the components are fully coupled to solve the fully-coupled equation of motion. Subsequently, the wet natural frequencies for various bending modes are identified. Then, the time histories and spectra of the girder's dynamic responses are presented and systematically analyzed. The second-order difference-frequency wave force and slowly-varying wind force may significantly affect the girder's lateral responses through resonance if the bridge's lateral bending stiffness is not sufficient. On the other hand, the first-order wave-frequency forces play a crucial role in the vertical responses.

• International journal of steel structures
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• v.18 no.5
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• pp.1639-1653
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• 2018

Bolted connections are suitable due to high quality prefabrication in the factory and erection in the workplace. Prefabrication and modularization cause high speed of erection and fabrication, high quality and quick return of investment. Their technical hitches transportation can be removed by prefabrication of joints and small fabrication of components. Box-columns are suitable members for bolted structures such as welded steel structures with moment frames in two directions etc., but their continual fabrication in multi-story buildings and performing the internal continuity plate in them will cause some practical dilemmas. The details of the proposal technique introduced here, is to remove such problems from the box columns. Besides, some other advantages include new prefabricated bolted beam-to-column connections referred to BBCC. This connection is a set of plates joined to columns, beams, support, and bolts. For a better understanding of its fabrication and erection techniques, two connection and one structural maquettes are made. The present work aims to study the cyclic behavior of connection numerically. To verify the accuracy of model, a similar tested connection was modelled. Its verification was then made through comparison with test results. The behavior of connection was evaluated for an exterior connection using three different support shapes. The effects of support shapes on rigidity, ductility, rotation capacity, maximum strength, four rad rotation strength were compared to those of the AISC seismic provision requirements. It was found that single beams support has all the AISC seismic provision requirements for special moment frames with and without a continuity plate, and box with continuity plate is the best support in the BBCC connection.

• Structural Engineering and Mechanics
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• v.85 no.2
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• pp.179-195
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• 2023

The performance of reinforced concrete (RC) beam specimens strengthened using a newly proposed Side Near Surface Mounted (S-NSM) technology was investigated experimentally in this work. In addition, analytical and nonlinear finite element (FE) modeling was exploited to forecast the performance of RC members reinforced with S-NSM utilizing steel bars. Five (one control and four strengthened) RC beams were evaluated for flexural performance under static loading conditions employing four-point bending loads. Experimental variables comprise different S-NSM reinforcement ratios. The constitutive models were applied for simulating the non-linear material characteristics of used concrete, major, and strengthening reinforcements. The failure load and mode, yield and ultimate strengths, deflection, strain, cracking behavior as well as ductility of the beams were evaluated and discussed. To cope with the flexural behavior of the tested beams, a 3D non-linear FE model was simulated. In parametric investigations, the influence of S-NSM reinforcement, the efficacy of the S-NSM procedure, and the structural response ductility are examined. The experimental, numerical, and analytical outcomes show good agreement. The results revealed a significant increase in yield and ultimate strengths as well as improved failure modes.

• Computers and Concrete
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• v.28 no.6
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• pp.533-547
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• 2021

Calculating the shear capacity of slender reinforced concrete beams without shear reinforcement was the subject of numerous studies, where the eternal problem of developing a single relationship that will be able to predict the expected shear capacity is still present. Using experimental results to extrapolate formulae was so far the main approach for solving this problem, whereas in the last two decades different research studies attempted to use artificial intelligence algorithms and available data sets of experimentally tested beams to develop new models that would demonstrate improved prediction capabilities. Given the limited number of available experimental databases, these studies were numerically restrained, unable to holistically address this problem. In this manuscript, a new approach is proposed where a numerically generated database is used to train machine-learning algorithms and develop an improved model for predicting the shear capacity of slender concrete beams reinforced only with longitudinal rebars. Finally, the proposed predictive model was validated through the use of an available ACI database that was developed by using experimental results on physical reinforced concrete beam specimens without shear and compressive reinforcement. For the first time, a numerically generated database was used to train a model for computing the shear capacity of slender concrete beams without stirrups and was found to have improved predictive abilities compared to the corresponding ACI equations. According to the analysis performed in this research work, it is deemed necessary to further enrich the current numerically generated database with additional data to further improve the dataset used for training and extrapolation. Finally, future research work foresees the study of beams with stirrups and deep beams for the development of improved predictive models.