Asymmetric Buildings Research Articles

The E-DVA method: A new approach for multi-modal pushover analysis under multi-component earthquakes

Pushover analysis is an incremental quasi-static procedure for evaluating the seismic behavior of buildings accounting for their non-linear behavior. The simplest and classical version of this method is based on the following assumptions: (i) the structure has a vertical plane of symmetry; (ii) there is a single horizontal earthquake component, parallel to the plane of symmetry; (iii) the structural dynamic behavior in this plane is governed by a dominant mode of vibration. These assumptions prevent asymmetric buildings to be accurately analyzed accounting for torsion effects. Moreover, even for symmetric structures and single component earthquakes, the effect of higher modes is not taken into account. In order to overcome these limitations, several multi-modal generalizations of the basic pushover analysis method have been proposed in the past years. In this paper, a new multi-modal approach is presented. Inspired by the Direct Vectorial Addition (DVA) method, the load pattern for the pushover analysis is defined as a linear combination of modal load patterns. The novel approach improves the original DVA by introducing an operative procedure for the calculation of modal combination factors (called “α-factors”). This Enhanced DVA (E-DVA) method is based on the notion of elliptical response envelopes and allows several earthquake components to be taken into account simultaneously. In addition, an approach is proposed for the identification of dominant modes and for their use into the definition of the pushover load pattern. Furthermore, this paper describes a method to obtain the equivalent Single-Degree-of-Freedom (SDoF) oscillator properties in the general multi-modal case under multi-component earthquake, with the corresponding factors for the capacity curve normalization. The definition of response spectrum for multi-component earthquakes is also given. For illustrative purposes, the E-DVA method is applied to a non-symmetric structure (SPEAR building), and the main results are presented and discussed.

Seismic Response of Mass Eccentric RC Framed Building

In the current study, six reinforced concrete framed buildings with various types of irregularities are designed in accordance with IS codes as test samples. Modal analysis, Response spectrum analysis, Push over analysis are performed on these structures and compare them with that of regular structures, shear forces and modal properties with the regular buildings that results variation in their behavior, which are considered the main causes of serious damage to the wrong plans of terraced buildings during earthquake. From this study, it finds that the asymmetric buildings shows that the maximum base shear for these different buildings are almost same. This is due to the base periods of all these buildings are almost uniform. The maximum results of the displacement of the roof for the symmetrical construction variant were found to be less differentiated from the two asymmetrical buildings for all cases studied here, which shows that the second asymmetric variant building is more acceptable than the first asymmetric variant building in all the cases. Code criterion for plan asymmetry building recommends that changing in the size of members of the structure or in the building but it has not mentioned that by giving eccentricity in opposite direction of the same structure where already eccentricity is available, it can reduce the plan asymmetry. To reduce eccentricity, variation in the stiffness dissemination can be very useful for such buildings.

Covalent organic framework mesocrystals through dynamic modulator manipulated mesoscale self-assembly of imine macrocycle precursors

Framework crystallization is an unresolved challenge in the chemistry of covalent organic frameworks (COFs) due to the poorly controlled simultaneous polymerization and crystallization processes. Here, we report the first morphogenesis of COF mesocrystals with two-dimensional hexagonal p6m symmetry through the combination of alkyl amine as a dynamic modulator and 2,4,6- triformylresorcinol imine as an asymmetrical building block. The amine modulator depresses the lateral growth of 2D sheets, and the slow kinetics combined with the asymmetrical conformation of 2,4,6-triformylresorcinol imine lead to the formation of transient imine macrocycles, which further undergo mesoscale self-assembly into nanotubular structures. The nanotubular structures tend to join together into rod-like bundles with ordered hexagonal rods, which finally grow into uniform hexagonal COF mesocrystals. The present strategy opens a nonclassical nucleation and crystal growth approach to create COFs with unexplored mesocrystal structures, which further extends the scope of crystalline framework materials and provides a new strategy for crystal morphogenesis.

Minimization of Torsional Parameters in Dual Asymmetrical Building through Proper Configuration of Centres

Columns are the core lateral load resisting elements in the buildings which do not have any other forms of resisting components. The sectional dimensions of the columns are often judge based upon the gravitational loading or a combined effect of gravitational and lateral loading on the structure. As per the early research on irregular buildings, they are highly vulnerable for damage when subjected to lateral forces (seismic/wind) when compared to regular shaped buildings, due to the presence of torsional forces. It has also been proved that these torsional forces are generated due to structural eccentricities of the system. The centres of stiffness and strength are predominantly dependent upon the configuration of the lateral load resisting elements. In this study, the effect of proper configuration of column’s dimensions on torsional parameters of irregular buildings is carried out. Non-linear Time History analysis on Plan irregular building with dual asymmetry is performed using scaled acceleragrams and the torsional parameters such are diaphragm’s rotation, torsional irregularity ratio, angular acceleration of the diaphragm are compared with the basic model.

Displacement-based seismic design with damage control of asymmetric buildings

Abstract This paper presents a procedure for the displacement-based seismic design of in-plan asymmetric buildings with earthquake-induced damage control. Damage is defined on the structural elements in the in-plan and elevation layout of the structure. The proposed method is based on the concepts of the performance-based seismic design philosophy and the application of basic equations of structural dynamics that are regularly used for the current design of buildings. In its application, the simultaneous bidirectional seismic demand is characterized by smooth design spectrum as proposed by most current regulations. To illustrate the steps required in the application of the design method proposed, the paper presents the design process of a 15- and 12-story buildings with in-plan asymmetric distribution of stiffnesses and subjected to a design demand given by the spectrum a real seismic event representative of soft soil sites such as those of the bed-lake of Mexico City. The results obtained are compared with the corresponding results of the nonlinear dynamic step-by-step analyses under the same seismic demand. Based on the results obtained, the relevance of this procedure in the displacement-based seismic design of asymmetric buildings and the implications for its consideration in future regulations are discussed. Graphical Abstract

Transition metal decorated soft nanomaterials through modular self-assembly of an asymmetric hybrid polyoxometalate.

An asymmetrically functionalised Wells-Dawson organic-inorganic hybrid polyoxometalate has been post-functionalised by Pt2+ coordination, and demonstrates self-assembly into surface-decorated micellar nanostructures. This multifunctional hybrid material is found to be a redox-active soft nanomaterial and demonstrates a new molecular design strategy with potential for applications in photo- or electro-catalysis.

Two new members in the quaternary Cs-Ag-As-S family with different arrangements of Ag-S and As-S asymmetric building units: syntheses, structures, and theoretical studies.

New functional materials of As-based multinary chalcogenidometalates have received special attention due to their different oxidation states and flexible building blocks. In this work, two new quaternary thioarsenates(iii), namely Cs2Ag2As2S5 (I) and Cs3AgAs4S8 (II), have been obtained by a simple surfactant-thermal technique. Their structures were determined on the basis of single-crystal X-ray diffraction; compound I belongs to the triclinic space group P1[combining macron] (no. 2) [a = 7.49(2) Å, b = 9.30(2) Å, c = 9.94(2) Å, α = 63.28(3)°, β = 82.11(3)°, γ = 87.78(3)°, V = 612.4(2) Å3 and Z = 2], whereas compound II crystallizes in the monoclinic space group C2/c (no. 12) [a = 27.76(6) Å, b = 6.98(2) Å, c = 19.68(4) Å, β = 109.85(3)°, V = 3586.7(2) Å3 and Z = 8]. Both structures are shown to feature two-dimensional (2D) layers with different arrangements of Ag-S and As-S asymmetric building units (ABUs). In compound I, the layer is constructed from vertex-sharing dimeric [As2S5] units linked by tetrameric [Ag4S8] moieties. The layered structure in compound II is formed by 21 helical chains based on [As4S9] groups which are further interconnected by tetrahedral [AgS4] chains. The analysis of the quaternary X-Ag-As-S (X = cations) system shows that various combination ways of Ag-S and As-S ABUs in these sulfides can be attributed to the cation-cation repulsion and stereochemically active lone-pair effect. The UV-vis/NIR absorption spectrum indicates that the optical band energy (Eg) of compounds I and II is 2.48 eV and 2.24 eV, respectively. Moreover, theoretical calculations indicate that the As-S and Ag-S bonding states determine the optical properties of the title compounds. This work not only enriches the structural chemistry of thioarsenates, but also opens up a new avenue for exploring novel multinary chalcogenidometalates.

The Effect of Foundation Flexibility on Probabilistic Seismic Performance of Plan‐Asymmetric Buildings with Different Strength Distributions

In this research, the probabilistic seismic performance of asymmetric reinforced concrete wall‐frame buildings with different strength distributions incorporating foundation flexibility effects is examined. By using probability‐based performance evaluation approach, it is possible to provide a more accurate prediction of the different strength distribution effect on the seismic performance of asymmetric buildings and find the most efficient strength distribution for meeting each performance level. These efficient distributions can be adopted in the performance‐based design of asymmetric buildings. For this purpose, first, the regression analysis and the concepts of efficiency and sufficiency were used to determine an optimal intensity measure (IM) for incremental dynamic analysis and evaluating the seismic response of the considered building models. Then, the proper magnitude of interstory drift capacity for this type of buildings in each limit state was estimated using the damage index concept. Finally, the effects of different strength distributions and the flexibility of foundation were studied on the seismic performance of the asymmetric buildings by investigating the mean annual frequencies of exceeding structural performance levels and confidence levels to satisfy performance objectives. It is concluded that irregular distributions of stiffness and strength in the plan of a building highly affect the seismic performance of buildings. Also, the results show that the optimum strength distribution is a function of the objective performance level and these optimum strength distributions are the same for both fixed‐ and flexible‐base conditions. Meanwhile, the flexible effect of foundation increases the mean annual frequencies of exceedance within the range of 10% to 45% and significantly decreases the confidence levels in most cases.

Seismic Assessment of Asymmetric Single-Story RC Buildings by Modified Pushover Analysis Using the “Capable Near Collapse Centre of Stiffness”: Validation of the Method

ABSTRACT A modification procedure on the standard pushover analysis for single-story asymmetric RC buildings, based on the “Capable Near Collapse Principal Reference System”, has been proposed recently. According to this procedure, the lateral static floor loading is applied eccentrically to the mass centre, using inelastic dynamic eccentricities plus any accidental ones. In this work, variations of a single-story building, about the static eccentricity and the torsional sensitivity, are examined, to verify this new pushover procedure comparing with the results of N-LRHA. The results of this parametric investigation show that the proposed procedure can safely predict the building’s stiff and flexible-side displacements.

Effect of using geopolymer flyash on torsion capacity of hybrid high-strength reinforced concrete beams containing fine and coarse aggregates substitution which added iron ores as filler

High demand for advanced infrastructure leads to the use of high-strength concrete. Complex, futuristic and asymmetrical building construction may create dangerous torsional load and moment, mainly due to earthquake. Using large amount of cement makes high-strength concrete not environmentally friendly. The use of natural aggregates continuously reduced its availability. Efforts to substitute cement and aggregate from abundant and environmentally-friendly natural materials could be smart solution. This study aims to analyze the torsional capacity of high-strength cantilever reinforced concrete beams having L configuration with a torque arm. Three hybrid beams were cast with substitution of 15% coal flyash (CFA), 15% palm oil blast furnace slag (POSFA) and 10% pozzolanic flyash (PFA) from cement weight, added with 10% pozzolanic sand as fine aggregate substitution and 40% palm oil blast furnace slag as coarse aggregate substitution. One beam without flyash and aggregate substitution (NPBHSC) was tested as comparison. All four beams added with iron ore as filler. The best torsion capacity achieved by PFA beam with maximum load (P) 2.83 ton, maximum torsion moment (M) 10.4 kNm, maximum torsion angle (Θ) 0.0225 rad, ductility (µ) 3.941 and cylinder compressive strength (σ) 59.48 MPa, when compared to NPBHSC beam which produced P = 2.65 ton, M = 9.638 kNm, Θ = 0.0069 rad, µ = 1.008 and σ = 44.40 MPa. POSFA beam followed then by CFA beam resulted in slightly smaller P and M, but generated greater σ, Θ and µ than NPBHSC. It can be concluded that geopolymer flyash can increase compressive strength, torsion capacity and ductility of high-strength reinforced concrete beams.

Role of Liquid Tuned Mass Dampers in Improving Torsional Competence of Asymmetric Buildings

Role of Liquid Tuned Mass Dampers in Improving Torsional Competence of Asymmetric Buildings

Performance of RC Asymmetrical Building With and Without Bracings by Linear Static and Time History Research

In asymmetrical Reinforce concrete (RC) buildings, the most effective and practical method of enhancing the seismic resistance and to reduce lateral displacement of the structures by combining bracings elements in the frame. Although past studies have focussed on the modelling of bracing elements, symmetric building models in linear analysis, there have been no detailed investigation on asymmetric structures under seismic excitation. Inclined elements (bracings) react as truss web elements which would bear compression or tension stresses. In present study a G+5 symmetrical RC bare frame, asymmetrical RC bare frame, asymmetrical RC frame incurred with different types of bracings such as X, V, inverted V, eccentric forward, eccentric back bracings at outer positions in all floors. Structural members of G+5 frame are designed as per the provisions of Indian seismic code IS: 1893 (Part-1)-2015. It was observed that maximum reduction both in X direction and Y-direction for x-type bracings in all models. It was observed that the maximum storey drift ratio of the structure under permissible limits as per the Indian seismic code IS: 1893 (Part-1)-2015 from linear static and dynamic analysis. From results obtained from linear static and dynamic analysis, the maximum forces in beams and columns reduced significantly X bracings in symmetric plan and asymmetric plan model

Stiffness and Damping Identification for Asymmetric Building Frame With In-plane Flexible Floors

In most building structures, floors with sufficient in-plane stiffness exist and an assumption of rigid in-plane stiffness is valid. However, in some building structures, an assumption of rigid in-plane stiffness does not hold. A method of system identification (SI) for physical parameters (stiffness, damping) is proposed for three-dimensional (3D) building structures with in-plane flexible floors. The stiffness and damping parameters of each vertical structural frame in the 3D building structure are identified from the measured floor horizontal accelerations together with the stiffness and damping parameters of each floor. It is shown that a batch processing least-squares estimation method for many discrete time-domain measured data enables the direct identification of both the stiffness and damping parameters of each vertical structural frame and the stiffness and damping parameters of each floor. The proposed method possesses an advantage that all stiffness and damping parameters of vertical frames and horizontal frames (floors) can be identified simultaneously without search iteration. The accuracy and reliability of the proposed method are made clear by numerical simulations for measured data without noise and measured data with noise. A method of noise elimination is proposed to enhance the identification accuracy. Finally, experiments using a shaking table are conducted for the accuracy investigation of the proposed identification method. It is confirmed that the proposed identification method possesses a reliable ability to identify the stiffness and damping parameters for 3D building structures with in-plane flexible floors.

Seismic response control of asymmetric buildings using tuned mass dampers

SummaryThe aim of the present study is to investigate the efficiency of the torsional tuned mass dampers (T‐TMDs) in response control of asymmetric buildings under bidirectional earthquake ground excitations. The efficiency of the T‐TMDs is compared with bidirectional tuned mass dampers (BTMDs). The T‐TMDs are oriented to the rotation of the structures about vertical axis with a single torsional mass attached to spring–dashpot elements, whereas the BTMD connects a single mass to two orthogonal sets of spring–dashpot elements oriented to principal axes of the building. The buildings are idealized three‐dimensional models with two translational and one torsional degrees of freedom for each floor. Three different configurations (cruciform‐shaped, L‐shaped, and T‐shaped) of multistory buildings are considered. The 5‐, 15‐, and 20‐story buildings with and without the tuned mass damper schemes are subjected to bidirectional earthquake ground excitation. In order to evaluate the effectiveness of the T‐TMDs and BTMD, the rotation, displacement, acceleration, and base shear force responses are computed. Parametric studies are conducted for all the configurations installed with the T‐TMDs and BTMD by varying their mass ratio, damping ratio, and ground motions. It is concluded that the T‐TMDs are more effective in mitigating the torsional response of asymmetric buildings as compared with the BTMD.

Multi-objective loss-based optimization of viscous dampers for seismic retrofitting of irregular structures

In this paper an efficient first-order multi-objective optimization scheme is adopted for the design of linear viscous dampers for the seismic retrofitting of frame buildings. A retrofitting cost function serves as one objective while the expected losses serve as the other objective. These two objectives are well understood by decision makers that may not be engineers. Furthermore, with the Pareto front for these two objectives at hand, the decision maker can make his decisions with the whole picture at hand. To allow achieving the Pareto front with a reasonable computational effort, a first-order multi-objective optimization approach is adopted. The gradients of the expected loss function, required for the optimization, are analytically derived using the very efficient Adjoint Variable method. This considerably improves the computational efficiency of the methodology. The efficacy of the framework is illustrated with a 2D four storey frame and an eight-storey 3D asymmetric building.

Structural reliability and performance evaluation of symmetric and asymmetric multi-storey buildings subjected to lateral wind forces

Lately there has been enormous enhancement of buildings architecturally. Most of the buildings are designed and constructed with diverse variations like soft–storey, torsional irregularity, asymmetrical layout of walls, irregularities in plan and elevation and thus overall building configuration. Any such variation result in challenging implications in terms of structural reliability and appropriate design of structural members. Calculation of lateral forces on these structures is an essential process in case of high– rise structures and structural performance of these aesthetically appealing asymmetric irregular shaped buildings especially when subjected to heavy wind forces need to be carefully assessed by structural engineers. The present work intends at performance evaluation by studying structural reliability of symmetrical and asymmetrical regular square, L, C and T–shaped reinforced concrete multi–storey buildings subjected to wind loads. The wind load analysis on these buildings is carried out in line with ASCE 7–10 design code. A comparative evaluation of critical parameters like fundamental period, natural and circular frequency of building, maximum joint displacement, storey drift ratio, inter–storey drift, internal forces in structural members, storey response and storey stiffness determines that difference in shape of a particular storey (or building) influence overall structural performance of building.

Surface-Confined Self-Assembly of Asymmetric Tetratopic Molecular Building Blocks.

Surface-confined self-assembly of functional molecular building blocks has recently been widely used to create low-dimensional, also covalent, superstructures with tailorable geometry and physicochemical properties. In this contribution, using the lattice Monte Carlo simulation method, we demonstrate how the structure-property relation can be established for the 2D self-assembly of a model tetrapod molecule with reduced symmetry. To that end, a rigid functional unit comprising a few interconnected segments arranged in different tetrapod shapes was used and its self-assembly on a triangular lattice representing a (111) crystal surface was simulated. The results of our calculations show strong dependence of the structure formation on the molecular symmetry, in particular on the (pro)chiral nature of the building block. The simulations predicted the formation of unusual ordered racemic networks with unique aperiodic spatial distribution of the surface enantiomers. Molecular symmetry was also found to have significant influence on the enantiopure self-assembly which resulted in the Kagome and brickwall networks and other less ordered extended superstructures with parallelogram pores. The theoretical findings of this contribution can be relevant to designing and on-surface synthesis of molecular superstructures with predefined geometries and functions. In particular, the predicted molecular architectures can stimulate experimental efforts to fabricate and explore new nanostructures, for example graphitic, having the composition and geometry proposed in our study.

Mass eccentricity effects on the torsional response of inelastic buildings

This paper investigates the role of accidental mass eccentricities on the inelastic torsional behaviour of multi-storey asymmetric buildings with a mixed type lateral load resisting system subjected to the Erzincan-1992 and Kobe-1995 ground motions. The numerical modelling results show that the effects of spatial variations of mass eccentricities are lower and smoother in the inelastic rather than the elastic state of deformation, but both the elastic and inelastic torsional response is pointing to the same optimum location of the key element for which the torsional response of the structure is minimized.

Estimation of accidental eccentricities for multi-storey buildings using artificial neural networks

Most of the research work on the torsional effect of the accidental eccentricity has been based on single-storey building models. Although the accidental eccentricity parameter is expressed for each individual floor, but the overall torsional behaviour of a multi-storey building can be significantly different from that of a single-storey model. In this context, a model of artificial neural networks (ANN) is elaborated to predict the accidental eccentricity in each floor of symmetrical and asymmetrical multi-storey buildings using acceleration or displacement records at the base and on the structure as well as the measured natural vibration frequencies of the structure. The database used for learning is constituted by varying randomly the live loads, the stiffness and the mass of the structural elements. The developed model is applied to eight standard multi-storey buildings. The calculated accidental eccentricities were in good agreement with the corresponding target accidental eccentricities. This generalized model for multi-storey buildings is an efficient tool to predict the real accidental eccentricities of such structures under different level of seismic loadings.

Incorporation of Torsional & Higher-Mode Responses in Displacement-Based Seismic Design of Asymmetric RC Frame Buildings

Direct displacement-based design (DDBD) is currently a widely used displacement-based seismic design method. DDBD accounts for the torsional response of reinforced concrete (RC) frame buildings by using semi-empirical equations formulated for wall-type buildings. Higher-mode responses are incorporated by using equations obtained from only a few parametric studies of regular planar frames. In this paper, there is an attempt to eliminate torsional responses by proportioning frames’ secant stiffnesses so that the centers of rigidity and supported mass (the mass on and above each story) coincide. Once the torsional rotations are significantly reduced and only translational motions are achieved, higher-mode responses are included using a technique developed by the authors in their recent paper. The efficiency of the proposed design procedure in fulfilling the intended performance objective is checked by two plan-asymmetric 20-story RC frame building cases. Case-I has the same-plan configuration while Case-II has a different-plan configuration along the height. Both cases have different bay widths in orthogonal directions. Verification of the case studies by nonlinear time history analysis (NTHA) has shown that the proposed method results in designs that satisfy the performance objective with reasonable accuracy without redesigning members. It is believed that a step forward is undertaken toward rendering design verification by NTHA less necessary, thereby saving computational resources and effort.