Improving the torsional response of asymmetric buildings with self-centering controlled rocking steel braced frame system

Self-centering controlled rocking steel braced-frame (SC-CR-SBF) is proposed as an earthquake-resistant system with low damage. Pre-stressed vertical strands provide a self-centering mechanism in the system and energy absorbing fuses restrict maximum displacement. Presence of asymmetry in structures can highlight the advantages of employing this structural system. Moreover, these days designing and constructing asymmetric and irregular structures is inevitable and as a result of architectural attractiveness and requirements of different functions of buildings, they are of great importance. Consequently, in these types of structures in order to minimize seismic responses, particular measures should be taken into consideration. Proper distribution of strength and stiffness throughout the plan of structures with self-centering systems can play a considerable role in resolving problems associated with asymmetry in these structures. In this study, the asymmetric buildings with 10% and 20% mass eccentricities and having different arrangements of centers were simulated. The models were analyzed under a set of 22 bidirectional far-field ground-motion records and corresponding responses of maximum roof drift, acceleration and rotation of the roof diaphragms of the structures with different arrangements of the center of mass, stiffness and strength were computed and studied. Results show that proper distribution of stiffness and strength throughout the plan of the structures with SC-CR-SBF system reduces the maximum roof drift as well as the rotation of the roof diaphragm. With appropriate arrangement of the centers, maximum drift response of the asymmetric structure decreases as much as roughly 20% and the ratio of the maximum drift response of the asymmetric structure to the response of the similar symmetric structure with the same overall stiffness and strength was 1.1. In other words, maximum drift response of the asymmetric structure with SC-CR-SBF system is acceptably close to the one for the symmetric building.

Damage Detection in Different Types of 3D Asymmetric Buildings Using Vibration Characteristics

This paper treats the vibration characteristics of three different types of asymmetric buildings and investigates the feasibility of applying an innovative vibration-based multicriteria approach-based damage index (MCA-DI) technique to detect the damage. This technique combines a modified form of the traditional modal strain energy method (MSEM) developed by decomposing the mode shapes into lateral and vertical components together with a modified form of the modal flexibility method to define a new damage indicator. Lastly, the dynamic behavior of three asymmetric building instances, including a 10-storey L-shaped structure, a 10-storey setback structure, and a 6-storey reinforced concrete structure with an unsymmetrical distribution of columns, was studied under five different damage scenarios. The results showed that despite different vibration characteristics of these three asymmetric buildings, the proposed method was able to accurately and effectively locate all damages and eliminate the confusion when more than one index is simultaneously used by using only the first a few modes.

Metamodel Approaches in Predicting the Seismic Response of Asymmetric Buildings

Asymmetry formed as a result of the eccentricity between the positions of Centre of Mass and Centre of Stiffness can cause undesired torsional coupling and can weaken the seismic performance of buildings and structures. This dynamic response is further affected by the randomness in material, geometric and loading properties caused as a result of uncertainties in construction and functioning. Stochastic analyses methods such as Monte Carlo Simulation have been found to accurately characterize this randomness and uncertainty, but are computationally intensive as well as expensive. This necessitates the need for alternative analyses methods that are much simpler and can fairly represent the uncertainties while preserving the similarity in results. The present investigation considers the various metamodel approaches in non-statistical stochastic analyses methods in determining the seismic response of asymmetric buildings. The study observes the efficiency of the High Dimensional Model Representation (HDMR) approach in accurately predicting the free vibration response of a reinforced concrete frame with the least number of samplings points as well as computational effort as compared to other response surface methods. For further validation, a non-linear reliability analysis was carried out at HDMR sampling points to obtain the seismic fragility of the building considered, the results of which satisfied the fragility obtained using conventional methods.

Optimum placement and design of multiple tuned mass dampers for vibration control of asymmetric buildings

This study proposed a design procedure to determine the optimal location, moving direction, and system parameters of multiple tuned mass dampers systematically for vibration control of asymmetric buildings under dynamic loadings such as earthquake or wind excitations. A piece of computer software was developed as a postprocessor of any commercial structural analysis programs, such as ETABS, SAP2000, and so on. First, the modal parameters of target building structure were extracted from its finite element model. The optimum location and moving direction of the multiple tuned mass dampers system are determined based on the controlled mode shapes and both modal participating mass ratio and modal direction factor. Then, the optimal parameters of the multiple tuned mass dampers system were calculated by minimizing the mean square modal displacement response ratio of the controlled mode for the target building with and without multiple tuned mass dampers system. To evaluate control effectiveness, the responses of the building with and without multiple tuned mass dampers system were compared in both frequency and time domains. The analysis results from a 5-story building with different torsion-coupling degrees and a 46-story real building show that the proposed multiple tuned mass dampers system is quite effective in mitigating excessive floor vibration, base shear, and elapsed time of vibration due to earthquake excitations to enhance both structural safety and resident comfort. It is also concluded that the torsion-coupling effect should be considered in determining the optimum planar location of multiple tuned mass dampers system which is equivalent to mass increase of the multiple tuned mass dampers system and thus improves the control efficacy for asymmetric buildings.

Torsional effects through mass asymmetry : A state-of-the-art review

Asymmetric distribution of mass over the floor slabs can cause torsional effects in buildings, even when it is symmetric in strength and stiffness. Such systems are referred to as mass eccentric or mass asymmetric buildings. Eccentricity in mass can result in building rotation in addition to its normal translation modes, which can further cause unpredictable deformation and even failure of the building under seismic loads. Irregularity in mass is found in buildings having concentrated mass elements in certain floors such as water tanks, machinery, etc. Many researchers have attempted to study the behavior of asymmetric buildings in general, but very few on the specific topic of mass asymmetry. This paper attempts to review and consolidate the literature written on the topic of mass asymmetry to the author’s knowledge.

Bidirectional Energy-based Pushover Procedure as a Fast Approach to Establish Approximate IDA Curves under Biaxial Seismic Excitations: An Evaluation for Medium- and High-rise Buildings

Bidirectional energy-based pushover (BEP) procedure is expanded in this paper to predict approximate incremental dynamic analysis (IDA) results of medium- and high-rise structures. BEP is a unique approach in the sense that it provides approximate IDA curves under the simultaneous effect of two horizontal components of ground motions and is applicable to both symmetric- and asymmetric-plan buildings. The method has already proved to be useful in low-rise buildings, and this study aims to evaluate its suitability for mid- and high-rise structures. Six structural models were considered in this evaluation in two groups of 9- and 20-story buildings, with each group consisting of a symmetric, a one-way asymmetric, and a two-way asymmetric-plan building. The results revealed that the method was sufficiently accurate to provide approximate IDA curves for all structural models. The method had similar accuracy in the asymmetric models as it did in the symmetric models, although the accuracy slightly decreased as the height of the building increased. BEP also provided good estimates of the demands in both ‘flexible’ and ‘stiff sides’ of the asymmetric buildings as well as the demands over the height of the buildings.