Summary
In this paper, concentric braced frames are combined with moment‐resisting frame (MRF) as a dual system subjected to near‐field (NF) pulse‐like and far‐field ground motions. The braced frame ...in this system configuration consists of steel buckling‐restrained braces (BRB model), braces with shape memory alloy (SMA model), or combination of BRB and SMA braces (COMBINED model). Some prototype structures of the proposed systems are designed according to the code recommendations. Then, the nonlinear models of the considered structures are developed in SeismoStruct software, and nonlinear time history analysis (NLTHA) is implemented. NLTHA is performed subjected to earthquake record sets at maximum considered earthquake (MCE) and design base earthquake (DBE) levels, and responses of the systems are investigated and compared with each other. Among the examined models, the SMA and COMBINED models exceed the CP level subjected to NF‐MCE record set. Therefore, more investigation is needed for using short‐segment SMA braces in the dual‐steel frames in NF area.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
AbstractThis study presents a deep convolutional neural network (CNN)-based approach to estimate the dynamic response of a linear single-degree-of-freedom (SDOF) system, a nonlinear SDOF system, and ...a full-scale 3-story multidegree of freedom (MDOF) steel frame. In the MDOF system, roof acceleration is estimated through the input ground motion. Various cases of noise-contaminated signals are considered in this study, and the conventional multilayer perceptron (MLP) algorithm serves as a reference for the proposed CNN approach. According to the results from numerical simulations and experimental data, the proposed CNN approach is able to predict the structural responses accurately, and it is more robust against noisy data compared with the MLP algorithm. Moreover, the physical interpretation of CNN model is discussed in the context of structural dynamics. It is demonstrated that in some special cases, the convolution kernel has the capability of approximating the numerical integration operator, and the convolution layers attempt to extract the dominant frequency signature observed in the ideal target signal while eliminating irrelevant information during the training process.
•Tests on a novel principle with kinked reinforced bars are reported.•Specimens include bars with various diameters, kinked heights, and lengths.•Various fracture and failure modes occurred in the ...connection types.•The kinked height should match the deformation capacity during beam cracking.•The plastic zone range and installation space should be considered for the length.
Various disasters may trigger a progressive collapse of frame structures, resulting in a high demand for new preventive structural strategies. Among the strategies adopted, increasing the joint rotation capacity to improve catenary action and forming a second path in the joint area are the most effective. In this study, a novel principle is proposed, in which the web opening is used to meet the rotation capacity, and kinked reinforced bars are installed in the beam–column joint to realize a second path. Experimental and numerical investigations were conducted on a frame substructure with kinked reinforced bars, considering their diameters, kinked heights, and lengths. The deformation capacity, vertical force vs. deformation response, failure mode, and contributions of the flexural and catenary actions on the reinforced bars were evaluated. The test results demonstrate that the kinked reinforced bars in the reduced-web-section connection (RRWS) specimens started to work after the plastic state. Although they had little influence on the flexural action, they were very important to the catenary action. When the kinked height a was less than 2d, the bearing capacity and ductility of the specimen increased with a, but further increasing the kinked height a beyond 2d would reduce both the bearing capacity and the ductility. In addition, the failure modes of the specimens were related to whether the plastic hinge was formed first or the reinforced bar had a major role first. Therefore, it is suggested to select the kinked height of the reinforced bar according to the deformation capacity of the beam, and the diameter of the bar as half of the kinked height.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
AbstractSteel frames may have an inherent ability to resist progressive collapse through alternative load-resisting mechanisms, including Vierendeel, flexural, catenary, and membrane actions. Among ...the columns at different positions, corner column failure caused by accidental loading is more dangerous due to the relatively few alternative load-resisting mechanisms. To evaluate the effects of infilled walls with or without openings on the progressive collapse resistance of steel frames, four two-span 2-story steel frames were tested in this study. According to the test results, the solid infilled frames achieved peak loads that were over 300% greater than those of the bare frame. Relative to the bare frame, the infilled frames with solid bricks and perforated bricks increased the deflection capacities by 15% and 29%, respectively. This result was attributed to the development of effective compressive struts in the infilled walls to partially transfer the vertical loads. Thus, premature joint failure was avoided. Moreover, the failure modes of the infilled walls changed when different types of brick were adopted. The infilled walls with solid bricks showed extensive shear sliding cracks; the infilled walls with perforated bricks were relatively intact, but the compressive corners were crushed. The partially infilled frame with a 40% opening ratio still increased the load-resisting capacity of the steel frame by 90%. In addition, the efficiencies of the compressive strut models of the infilled walls under corner column loss conditions were evaluated. Based on the calculations, the width of the equivalent compressive strut provided by current US standards is recommended.
AbstractThe dynamic effect of structures under column removal scenarios is investigated by conducting comparative experiments on two identical steel frames with concrete slabs. One frame suffers from ...a static edge-column loss, while the other is subjected to a dynamic column loss that is simulated by imposing an impact on a three-hinged column. The vertical deflections at the column-removal location of the two frames are reported and compared. The stress measurements at key locations of the frame in the static test are also presented. Numerical models are created and validated against experimental results. To quantify the dynamic effect of structures under a sudden edge-column loss, a dynamic amplification factor (DAF) is analytically determined based on the principle of energy conservation and is verified against validated numerical analyses. Parametric studies are also conducted on DAFs for various deflections and stiffness ratios. The experimental results suggest that the two orthogonal steel beams intersecting at the column-removal location deform linearly. The double-span beam after column loss suffers more external loads than the cantilever beam perpendicular to it. The positive yield lines diagonally distribute at the slab bottom, extending from the column-removal location to the corners of the slab. It is found that, owing to the dynamic effect, the ultimate bearing capacity of the frame in the test decreases by approximately 25.6% under a sudden edge-column loss scenario. The discrepancies between the dynamic and static deflections are intensified when the initially imposed gravity loads increase. The DAF at the ultimate limit state of composite frame structures due to a sudden edge-column loss can range from 1.15 to 1.4. Ignoring the enhancement of membrane and catenary action to the resistance can result in an underestimation of the dynamic effect of frames at large deflections. The method for calculating DAFs proposed by Department of Defense is not conservative in practical safety design since a monotonously decreasing value is designated.
•The paper shows study of steel-framed subassemblies against falling-debris impact.•The accuracy of numerical model is verified against previously impact tests.•The effect of Span-to-Depth Ratio on ...impact resistance was investigated.•A simplified approach was proposed to assess the impact resistance of structures.
Up to now, most studies corresponding to building structures against progressive collapse are based on the column-removal scenario. However, other cases, i.e., falling-debris impact scenario, which may cause progressive collapse of building structures were limitedly studied. This paper presents numerical simulations and a simplified approach of steel-framed subassemblies with Reverse Channel connection with Extended End Plate (RC-EEP) under the falling-debris impact scenario. The numerical results demonstrate the ductility, load-carrying capacity, and energy-absorption capacity of the steel-framed subassemblies with different Span-to-Depth Ratio under various impacted locations. All specimens showed the same global deformation profile and same load-resistance mechanism under the impact load on the same locations. Under mid-span-impact scenario, axial elongation of connection primarily affected the ductility. Both catenary action and flexural action affected the load-carrying capacity. Failure displacement, maximum load-carrying capacity and energy-absorption capacity all decreased with the increase of the Span-to-Depth ratio. Under beam-end-impact scenario, both the ductility and the load-carrying capacity were primarily controlled by the shear deformation and shear strength of the connection close to the impacted location. The increase of the Span-to-Depth ratio had little effect on failure displacement while slightly reduced the maximum load-carrying capacity and energy absorption capacity. Smaller Span-to-Depth Ratio was recommended in the impact-resisting design for impact load on both impact locations. A simplified approach was also developed to predict the behaviour of the steel frame subassemblies up to total failure. The validation study indicated that the proposed models can represent the key responses of steel-framed subassemblies with different Span-to-Depth Ratio subjected to impact load on various locations, including the flexural action at pure bending stage, the development of flexural action and catenary action at the tension-bending stage, and the failure stage. The accuracy of the proposed approach was validated against the experimental tests and numerical simulations, in the aspects of internal force-displacement relationships, load-carrying capacity-displacement relationships, and energy absorption-displacement relationships. The proposed approach provided an accurate and efficient way to predict the impact resistance of specimens with various Span-to-Depth Ratios under both of the mid-span impact and the beam-end impact scenarios.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
AbstractA seismic retrofit method using external steel frames was studied for old RC buildings with nonseismic details. To verify the external retrofit method, 2-story frame specimens were tested ...under cyclic lateral loading. The test results indicated that the external steel frame successfully enhanced the stiffness and strength of deficient RC moment frames without deteriorating the deformation capacity. The energy-dissipation capacity was also improved by restraining early failure of the RC beam-column joints. The failure mode of the retrofitted frames was governed by the flexural mechanism of the first-story RC columns, with partial yielding of the upper structure. The RC columns were subjected to additional axial forces that were transferred from the external steel frame, in which the steel columns were not extended to the foundation. The strengths of retrofitted frames were evaluated by two approaches based on the frame plastic hinge mechanism: (1) the sum of the strengths of independent RC and steel moment frames, and (2) the strength assuming full composite section of concrete and steel members. On the basis of the test results, design considerations for the external steel frame-retrofitting method are recommended.
•An autoencoder based framework for structural damage identification is proposed.•It supports deep neural networks for solution of pattern recognition problems.•Dimensionality reduction and ...relationship learning are included in the framework.•Accurate identification results are obtained considering uncertainties and noises.•Numerical and experimental investigations are conducted to validate the approach.
Artificial neural networks are computational approaches based on machine learning to learn and make predictions based on data, and have been applied successfully in diverse applications including structural health monitoring in civil engineering. It is difficult to optimize the weights in the neural networks that have multiple hidden layers due to the vanishing gradient issue. This paper proposes an autoencoder based framework for structural damage identification, which can support deep neural networks and be utilized to obtain optimal solutions for pattern recognition problems of highly non-linear nature, such as learning a mapping between the vibration characteristics and structural damage. Two main components are defined in the proposed framework, namely, dimensionality reduction and relationship learning. The first component is to reduce the dimensionality of the original input vector while preserving the required necessary information, and the second component is to perform the relationship learning between the features with the reduced dimensionality and the stiffness reduction parameters of the structure. Vibration characteristics, such as natural frequencies and mode shapes, are used as the input and the structural damage are considered as the output vector. A pre-training scheme is performed to train the hidden layers in the autoencoders layer by layer, and fine tuning is conducted to optimize the whole network. Numerical and experimental investigations on steel frame structures are conducted to demonstrate the accuracy and efficiency of the proposed framework, comparing with the traditional ANN methods.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Quasi-static cyclic test on a half-scaled two-story steel pendular frame with CSB.•CSB is a yielding steel bracing element characterized by a boomerang-like shape.•Optimal combination of stiffness, ...strength, ductility, moderate hysteretic damping.•Feasible solution for braced frames to meet multiple seismic performance objectives.•Connection plates play a non-negligible contribution in the structural response.
This paper presents the first main results of quasi-static cyclic tests performed on a half-scaled two-storey one-bay steel pendular frame equipped with Crescent Shaped Braces (CSBs).
The CSB is a yielding steel bracing element characterized by a boomerang-like shape, designed to provide the structure with an optimal combination of lateral stiffness, strength, ductility capacity and hysteretic dissipation, thus capable of meeting multiple seismic performance objectives within the context of Performance Based Seismic Design. In previous research studies, the behaviour of single CSBs under cyclic loads was analytically, numerically, and experimentally investigated through tests conducted on 1:6 scaled specimens. These results verified the potential capabilities of the device.
As a further step of the experimental validation, a set of tests have been designed to evaluate the performances of CSBs when inserted into realistic frame structures. A two-storey prototype structure has been designed to meet selected seismic performance objectives, which could not be achieved with traditional diagonal braces. From that, a single-bay two-storey frame, representative of one braced frame of the whole structure, has been designed, detailed, and manufactured (half-scaled) for the experimental tests. For a full assessment of the behaviour of the braced frame, two configurations have been designed and tested. This paper presents the results of the test performed on the first configuration with one CSB device placed at the first storey only. The attention has been mainly focused on the global force-displacement response and the contribution of the connection plates, energy dissipation capacities and local strains around the knee-point region of the CSB. The results show that the CSB behaves following the theoretical predictions, while the connection plates provide a non-negligible contribution in the whole response of the system that should be properly accounted for in the design phase.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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•A machine learning-based framework for deriving state-dependent fragility curves for existing steel moment frames was presented.•Feedforward neural network classification models were ...utilised to predict the damage state of existing steel frames with respect to prescribed limit states.•The influence of masonry infills on the seismic response of existing steel moment frame was considered.•Four Pre-Northridge steel frames covering low- and med-rise buildings designed for low and high seismicity were adopted to demonstrated the proposed framework.
Seismic assessment of existing buildings is usually a building-specific task that relies on refined finite element models. Such a task may require considerable computational demand, especially when predicting the seismic fragility of existing buildings under the framework of performance-based earthquake engineering. However, the computational cost can be significantly reduced by replacing the finite element model with a well-trained machine learning-based model, for example, an artificial neural network model. This paper presents the application of feedforward neural networks to derive the state-dependent fragility curves of existing steel moment frames, taking into account the effects of masonry infills. The network models can be trained to predict explicitly whether a structure exceeds the target limit state based on representative intensity measures of ground motions, which is in nature a binary classification problem. The number of non-linear time-history analysis required to generate the training data for the network models tends to be significantly lower compared to the case of conventional incremental dynamic analysis, particularly when a great number of ground motions are adopted aiming at higher accuracy of the fragility curves.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
