Building Design Codes Research Articles

Risk-adjusted design basis earthquake: a case study of Tehran megacity

The basic goal of earthquake resistant building design codes is to provide life safety in the event of extreme earthquake loading and to reduce the seismic risk in the long run. In the most building codes including Iranian building code (Standard No. 2800), design basis earthquake is defined as an earthquake with 10% probability of exceedance (PE) in 50 years. Such an approach leads to buildings with unknown reliability, meaning that the probability of exceedance from the specified limit states in the service lifetime is not known. Furthermore, the regions with the same mapped peak ground acceleration (PGADBE) and different hazard curves, may have different seismic risks. Therefore, life safety is not uniformly provided across the entire region. Here, an attempt is made to estimate PGADBEs based on the uniform collapse risk approach for Tehran megacity. The building capacity and PGA hazard curve for 354 grids in Tehran are computed. Then, the risk-adjusted design PGA at different grid points are calculated by optimizing risk integral using the acceptance criteria of 1% in 50 years for ordinary usage buildings (risk category II). The computed risk-adjusted design PGAs vary from 0.33 g in the east to about 0.45 g toward west, south, and north. Meanwhile, the proposed mapped PGADBE in standard 2800 is a constant value of 0.35 g for the whole region. To preserve a uniform collapse risk, risk-adjustment factors to modify the mapped PGADBE are introduced. Furthermore, the maximum considered earthquake (MCE) required to evaluate the acceptance criteria is found to be in the range of 1.5% to 2.5% PE in 50 years. The PGAs with 2% PE in 50 years provide nearly uniform acceptable probability of collapse for buildings classified in risk category II. In addition, it is found that the buildings’ seismic importance factor (I) also needs to be revised from 1.2 to 1.3 for seismic risk category III, and from 1.4 to 1.6 for seismic risk category IV to preserve the 0.5% and 0.25% collapse risk in 50 years, respectively. The outcomes also revealed that the sensitivity analysis with regard to the uncertainty of buildings’ collapse fragility curve can be ignored for buildings in risk categories I and II, while it needs to be performed for buildings in risk categories III, and especially IV. Finally, the estimated PGA hazard curves of the Tehran megacity are approximated by the cubic functions to expedite the future risk assessment studies in Tehran megacity.

Geotechnical advances in development of a seismic code for Hong Kong

Hong Kong is located in a low- to moderate-seismicity region with earthquake damage to buildings having been recorded in the past. On average, there are about two earth tremors felt every year. Nowadays, the city is a unique place in the world with a high-density population living in high-rise buildings and surrounded by steeply sloping terrain. The potential risk of earthquake-induced damage thus calls for the development of a seismic design code for buildings in Hong Kong. In recent years, several critical geotechnical studies have been completed focusing on enhancing earthquake resilience in Hong Kong. They have included: (a) updating of probabilistic seismic hazard assessment based on a recent earthquake catalogue; (b) examination of local site effects and topographic amplification effects based on a pilot-area-specific seismic microzonation study; (c) reviewing the earthquake-induced landslide susceptibility of the natural terrain; and (d) assessment of the seismic stability of man-made slopes and retaining walls. These seismic studies are pivotal to the development of the seismic design code which is being pursued in Hong Kong. This paper is an important milestone in providing a detailed account of these studies and their impact on the code development.

Comparative Study of DAM and ELM to One-Storey Eccentrically Braced Frames Subjected to Seismic Load in Indonesia

Indonesia is late in updating its structural steel building design code to AISC 360-10. Revision was done in 2015 replacing the 2002 code. The new version changes the method of steel stability analysis from effective length method (ELM) to direct analysis method (DAM). The 2015 code implements DAM, which is based on second-order elastic analysis which directly calculates P-delta effect in analysis. DAM takes into account geometric imperfection and strength reduction. Notional load as 0.002 of gravity load should be applied horizontally to represent geometric imperfection. It is allowed to adjust the notional load coefficient. Numerical study has been conducted to compare the use of DAM and ELM on eccentrically-braced frame subjected to Indonesian seismic load. Different values of notional load coefficient are considered. Experimental results conducted by other researchers were used as reference. The frames were reanalysed using four different stability methods: ELM first-order analysis, ELM second-order analysis and DAM with different notional load coefficients: 0.002 and 0.003

Fatigue damage analysis of steel components subjected to earthquake loadings

PurposeExamination of steel moment resisting frames after the 1994 Northridge earthquake showed fatigue cracks presented in the beam–column connections of the frames. These observations indicate that fatigue failure may occur in the steel components of building structures in an earthquake event. To apply the fatigue design approach using the Palmgren–Miner’s rule for steel components of the moment resisting frames requires the knowledge regarding the damage index value at fatigue failure. The purpose of this paper is to perform fatigue tests to give the first damage values of steel components subjected to real earthquake-induced loadings.Design/methodology/approachThe added-damping-and-stiffness steel plates which are used in building structures for earthquake mitigation were fabricated and tested by constant amplitude, SAC block and earthquake-induced loadings to failure. The earthquake loadings were obtained from the dynamic analysis of a steel frame with the mentioned plates. The load cycles of the SAC block and the calculated earthquake loadings were counted using the rainflow-counting method, and the damage index value of each specimen were calculated using the Palmgren–Miner’s rule.FindingsReverse stiffness obtained from cyclic load-displacement loops is a robust and consistent parameter that can be used for determining fatigue failure of tested components. The Palmgren–Miner’s damage values at failure, caused by earthquake loadings, are smaller than 1, and in addition, are also smaller than those obtained from the tests of the SAC block loading. The large-amplitude cycles in the earthquake loading produce large damage on the specimens, and intermediate range cycles also produce damage that should not be neglected in the fatigue analysis.Originality/valueToday’s building design code allows large plastic deformation to occur in steel frames during an earthquake. However, the pre-Northridge earthquake steel frames showed fatigue cracks without the expected substantial plastic deformation at beam flanges. Proposed solutions to this problem were the reduced beam section neglecting the existence of the cracks at beam–column connections. This study considered the fatigue phenomenon in steel frames and provided the first set of tested fatigue damage values for steel components subjected to realistic earthquake loadings, which offered a possible method of dealing with fatigue cracks in the steel components of a building structure.

A Study on Risk Assessment and Analysis Method of Buildings for the Development of Korean Integrated Disaster Evaluation Simulator (K-IDES) in High-Rise Buildings

The purpose of this study is to develop a platform tentatively named the Korean Integrated Disaster Evaluation Simulator (K-IDES) to assess building risk during disasters. In this study, the first step includes an analysis of FEMA’s risk management series in the USA for precedent research. Among them, FEMA IRVS is selected as the case study for the development of the K-IDES framework and through the comparative analysis of domestic building design guides, codes, and special acts related to disasters. The next step is to develop a risk assessment methodology to yield quantitative results. This methodology consists of classification systems, calculation methods, and grade ratings. Based on it, K-IDES will establish a management system that can systematically integrate the collected information by using assessment techniques for elements except legal standards to measure risks in response to various disasters and present a classification system of evaluation factors, criteria for evaluation items, and risk assessment methods. In the next study, and through the simulation of the selected buildings by using this risk assessment, a check-list will be verified. The final goal of this study is to build a platform to be used as an integrated risk management method against a complex disaster by the expansion to other types of buildings through continuous data scaling and management systematization.

The contested geographies of master planned estates: the role of the building design codes

ABSTRACTMuch of the debate in contemporary urban studies has surrounded the provision of affordable housing in capital and regional cities. Master planned estates (MPEs) have emerged as the dominant form of housing in Australia. Master planned estates often include private governance mechanisms to regulate resident behaviour and building designs, improving the sales potential and creating an enhanced living environment for residents. Using case studies of three MPEs this paper explores aspects of the building design codes (BDCs), including their rationale, contribution to initial engagement and resident experiences. It finds that while the BDCs are perceived as integral to improving estate sales and the long-term operation, the developer’s commitment declines over time. The BDCs help to attract new residents by creating predictability. The estate residents are largely supportive of the BDCs and some feel abandoned when the developer’s commitment declines. The results are interpreted through a commodity perspective, which considers how the moments of production, exchange and consumption are inflected through culturally derived notions of home and home-making processes.

Shake table tests of different seismic isolation systems on a large scale structure subjected to low to moderate earthquakes

Abstract Seismic isolation systems designed for extreme events may likely experience low to moderate earthquakes during the design life of the structure rather than the extreme event itself. In new seismic building design codes, low and moderate earthquakes are also mandatory to be investigated in Turkey and some other countries. One of the main reasons is to protect the integrity of non-structural elements or machines during these types of earthquakes. The selection of appropriate seismic isolation is typically decided based on their force-displacement characteristics and amount of energy dissipation per cycle. The same energy dissipation per cycle (EDC) can be achieved by high force-low displacement or low force-high displacement response. The focus of this research is given to identify the performance of ball rubber bearing isolation systems compared to different or similar EDC units such as elastomeric bearings and lead rubber bearings through a series of shake table tests performed at low to moderate earthquake levels. Shake table tests were conducted on an almost full scale short span bridge. The tests have revealed that the ball rubber bearings are superior to elastomeric bearings in terms of EDC and can match EDC of LRB. However, although LRB and BRB have the same EDC, BRB is more beneficial to use under low to moderate earthquakes since BRB can transmit less force with larger displacement compared to LRB and LRB can sometimes stay in elastic range with an ineffective EDC as a stiffer elastomeric bearing.

Advanced two-step integrated optimization of actively controlled nonlinear structure under mainshock–aftershock sequences

In this paper, an attempt is made to examine a new method for designing and applying the active vibration control system to improve building performance under mainshock–aftershock sequences. In this regard, three different structures are considered; 5-, 10-, and 15-story buildings. Seven mainshock–aftershock sequences are selected from the Iranian accelerogram database for analyzing the structures. By implementing an advanced two-step optimization method, buildings equipped with the active vibration control system (linear–quadratic regulator (LQR) algorithm) are designed to withstand all events of mainshock–aftershock sequences. In the first optimization step, a multi-objective optimization with the genetic algorithm is performed and a set of optimal Pareto front results is obtained. In the next step, the life-cycle cost of each optimal design sample of the Pareto front is calculated by considering the cumulative damage and the design sample with the minimum cost is selected as a final optimal property. The results prove that the active vibration control system is capable of reducing structural responses, including acceleration, drift, and residual drift under mainshock–aftershock sequences, and consequently the life-cycle cost of buildings, especially the taller ones. In addition, obtaining the building design variables (story stiffness and yielding force) and active LQR algorithm properties simultaneously leads to a slightly softer final building model than the conventional structure designed by the common building design code. Moreover, it is revealed that, by considering the aftershocks, the building life-cycle cost increases significantly.

Capacity design: Early history

SummaryThe paper documents the little‐known story behind the development of the concept of capacity design and sheds new light regarding the individual contributions, which led to it becoming an important design tool for the control of inelastic response. The basic concept was laid out in the 1961 book by Blume, Newmark, and Corning, Design of Multistory Reinforced Concrete Buildings for Earthquake Motions, with the notable sections written by Mete Sozen; the basic concept was included in the 1967 to 1968 revision of the Structural Engineers Association of California (SEAOC) recommendations. John Hollings, a prominent structural designer in New Zealand, quoted the SEAOC recommendations and Blume, Newmark, and Corning when he used these ideas in a design procedure he proposed in 1968 to 1969 for the control of the inelastic response in concrete buildings. The term “capacity design” for that procedure seems to have been coined by a select team of structural designers of New Zealand's public buildings under the leadership of Otto Glogau, who had already introduced the new SEAOC rules in the 1968 New Zealand design code for public buildings. Tom Paulay is credited with publicizing and further development of capacity design as a holistic approach for the control of inelastic response. He was instrumental in disseminating the concept, especially in Europe, and often is called the “father” of capacity design.

Optimization of reinforced concrete frames subjected to historical time-history loadings using DMPSO algorithm

In this paper, the seismic design of reinforced concrete (RC) frames subjected to time-history loadings was formulated as an optimization problem. Because finding the optimum design is relatively difficult and time-consuming for structural dynamics problems, an innovative algorithm combining multi-criterion decision-making (DM) and Particle Swarm Optimization (PSO), called DMPSO, was presented for accelerating convergence toward the optimum solution. The effectiveness of the proposed algorithm was illustrated in some benchmark reinforced concrete optimization problems. The main goal was to minimize the cost or weight of structures subjected to time-history loadings while satisfying all design requirements imposed by building design codes. The results confirmed the ability of the proposed algorithm to find the optimal solutions for structural optimization problems subjected to time-history loadings.

Common Structural Details and Deficiencies in Indonesian RC Buildings: Preliminary Report on Field Investigation in Padang City, West Sumatra

Significant damage to reinforced concrete buildings by the 2009 Western Sumatera Earthquake revealed that deficiencies in design engineering and/or construction practice existed. This indicated that enforcement of building design codes was lacking. The Indonesian government has updated the building design codes which should have been applied in the construction of new buildings. However, enforcement of these codes on design engineering and/or construction practice in Padang city is not clear. In this study, a field investigation was performed to investigate common structural details and deficiencies in newly constructed multi-story reinforced concrete buildings. The investigation was conducted through visiting building construction sites in Padang city area. This study preliminary reports the investigation results on 39 private buildings and 8 government buildings. The common deficiencies found on the investigated buildings were low material quality, small structural dimensions with light longitudinal reinforcement, insufficient transverse reinforcement with poor details, improper location of lap splice of rebar, lack of hoops inside exterior and interior beam-column joints, and deficient anchorage of beam reinforcement to exterior beam-column joints. These investigation results clarify that enforcement of the latest buildings design codes in design engineering and/or construction practice is still lacking in the investigated area.

Influencia del tipo de rótula plástica en el análisis no lineal de estructuras de hormigón armado

An adequate modelling of the plastic hinges generated during the pushover analysis is crucial in order to obtain accurate results. Thus, empirical expressions must be used appropriately in order to model the generalised force-deformation relationship of plastic hinges. The main aim of this article is to study the influence of different plastic hinge models on the non-linear structural behaviour of reinforced concrete structures. To that end, several non-linear analyses have been performed using the following plastic hinge models: the model included in the code FEMA-356 and two additional models developed by some researchers by using empirical expressions calibrated with different experimental data. The results obtained show that plastic hinges modelled with empirical expressions can be used to more precisely model the behaviour of structural elements in ordinary buildings located in seismic areas, and to compare with the results offered by the models included in seismic building design codes.

Reliability of partially encased steel-concrete composite columns under eccentric loading

Abstract The Brazilian design code for composite buildings (NBR8800) has never been subject to a reliability-based calibration of the partial factors used in design. As a consequence, the level of structural safety achieved by using these factors is, in general, unknown. This paper presents a study of the reliability of partially encased steel-concrete composite columns, subject to compression and bending. Literature statistics are used to quantify uncertainty in strength of structural materials and in loads. Reliability indexes are evaluated, via FORM, for two ratios between dead and live loads, and for some values of load eccentricity. It was found that larger load eccentricity leads to a reduction in reliability indexes. These values are larger than minimum values recommended in international design codes; hence one concludes that design of such columns using NBR8800 leads to acceptable safety levels.

Performance of Direct Displacement Based Design on Regular Concrete Building Against Indonesian Response Spectrum

The renewal of Indonesian seismic code from SNI 1726-2002 into SNI 1726-2012 brings significant change in the design spectrum. Focused on several regular plan concrete building which have been design using displacement based design method, the aim of this study is to verify their performance using nonlinear time history analysis based on parameters: drift, damage indices, and plastic mechanism determined by FEMA 356. The excitation is spectrum consistent accelerogram based on El-Centro 1940 N-S, to match with the new Indonesian response spectrum for soft soil in low- and high intensity area. It is found that the code-designed buildings are not suitable for the targeted design of level-2 with maximum drift of 2.5% due to major. This is caused by improper selection of SNI spectrum as the design major earthquake. In fact, it is only equivalent to small earthquake. Although buildings survive up to a very rare earthquake without collapse but they suffer excessive damage and rotation due to small- to major-earthquake. The capacity design procedure is able to maintain ductile mechanism, but some columns experience yielding at prohibited locations.

Characteristic ground motions of the 25th April 2015 Nepal earthquake (Mw 7.9) and its implications for the structural design codes for the border areas of India to Nepal

The 25th April 2015 Nepal Earthquake was found associated with a series of aftershocks, and the mainshock rupture propagated predominantly towards SE direction where a major aftershock (Mw 7.3) rocked on 12th May 2015 to the east of the mainshock that enhanced the rate of occurrence of aftershocks in the affected region. We conducted a rigorous analysis of strong motion data to understand the characteristics of ground motion and their bearing on the structural design codes, responsible for the damage to the structures in the border area of India to Nepal. The effect of ground geology on the acceleration response spectra are also evaluated using main shock and its associated strong earthquakes. All the sites used in the present analysis are located on alluvium deposits showing a predominant period of 0.242sec for horizontal components and at 0.193sec for vertical components. Our results demonstrated that observed Peak Ground Acceleration (PGA) has prominent distribution in the border cities of UP and Bihar. PGA ranges from 3 to 80cm/sec2 in the study region for the epicentral distance varying from 120km to 495km with respect to the source zone (mainshock). The Peak Ground Velocity (PGV) varies from 1 to 16cm/sec while the Peak Ground Displacement (PGD) lies in between 1cm and 20cm for the same area. Our study shows that variation of PGD, PGV, and PGA are controlled and dictated by the geo-morphological constraints, besides the nature and extent of structural heterogeneities of the sub-surface geological formation materials. The obtained normalised spectral amplifications are compared with the Bureau of Indian Standard code for construction of buildings which shows that the current Indian building design code is within the structural limits proposed for the seismic forces at all periods for alluvium sites, suggesting that the structural heterogeneity has the strong role contributing towards the intrinsic attenuation in the seismic wave propagating medium. Our analysis also shows a good correspondence with the nonlinearity of the seismic waves, which in turn controls the degree of damage in an area. We infer that extent of damage to the structures in the border cities of India, vicinity to the rupture zone can be avoided if the existing building design code could have been implemented as the earthquake risk resilient mitigation plan.

Prediction of fundamental period of regular frame buildings

The most important structural parameter in the estimation of the seismic demand on a building is the natural period of the building’s fundamental/first mode of vibration. There are several existing empirical, analytical, and experimental methods which can be used to estimate the fundamental period of a building. The empirical equations prescribed in the building codes are simple, but they do not consider actual building properties, and are very approximate. On the other hand, analytical methods like Eigenvalue analysis and Rayleigh method are able to consider most of the structural parameters that are known to affect the period of a building. Nevertheless, the analytical methods require considerable effort and expertise; often requiring structural analysis software’s to estimate the fundamental period of a building. In this paper, a generic method is developed to estimate the fundamental period of regular frame buildings and a simple yet reliable equation is proposed. The equation is derived using the basic concept of MacLeod’s method for estimation of roof/top deflection of a frame building, which is modified to more accurately predict the lateral stiffness of moment resisting frames under triangular lateral force distribution typically used in seismic design and analysis of frame buildings. To verify the reliability and versatility of the developed equation, the fundamental periods predicted are compared with the periods obtained from Eigenvalue analysis for a large number of low to medium rise RC frame buildings. The fundamental period predicted using the proposed equation is also verified using the period obtained using the Rayleigh method and measured in experimental tests. Since the proposed equation was found to closely predict the fundamental period, the results are used to study the limitations of the empirical equations prescribed in building codes. The applicability of the proposed equation to predict the fundamental period of low to medium rise frame buildings with minor irregularity is also investigated, and it was found that the proposed equation can be used for slightly irregular frame buildings without inducing any additional error. The proposed equation is simple enough to be implemented into building design codes and can be readily used by practicing engineers in design of new buildings as well as assessment of existing buildings.

Influence of adjusted models of plastic hinges in nonlinear behaviour of reinforced concrete buildings

Among the procedures available for the seismic analysis of structures, pushover analysis is one of the most frequently used methods by structural engineers. An adequate modelling of the plastic hinges generated during the pushover analysis is crucial in order to obtain accurate results. Thus, the yielding and ultimate states of the cross-section must be defined in order to model the generalised force-deformation relation of plastic hinges. For this purpose, the use of empirical expressions that obtain the aforementioned states from the cross-section properties can prove beneficial.The main objective of this work is to study the influence of different plastic hinge models on the structural nonlinear behaviour of reinforced concrete structures. To that end, several nonlinear analyses have been performed with the software SAP2000®, considering the following plastic hinge models: (i) the model of FEMA-356 included in SAP2000®, and (ii) two additional models developed by some researchers by using empirical expressions calibrated with different experimental data. Simplified structures of two buildings have been used as examples.The results obtained show that plastic hinges modelled with empirical expressions can be used by structural engineers to more precisely model the behaviour of structural elements in ordinary reinforced concrete buildings located in seismic areas, and to compare with the results offered by the models included in seismic building design codes.

Evaluation of seismic performance factors for steel DIAGRID structural system design

This article presents a proposed analytical methodology to determine seismic force-resisting system R-values for steel diagrid framed systems. As current model building codes do not explicitly address the seismic design performance factors for this new and emerging structural system, the purpose of this study is to provide a sound and reliable basis for defining such seismic design parameters. An approach and methodology for the reliable determination of seismic performance factors for use in the design of steel diagrid framed structural systems is proposed. The recommended methodology is based on current state-of-the-art and state-of-the practice methods including structural nonlinear dynamic analysis techniques, testing data requirements, building code design procedures and earthquake ground motion characterization. In determining appropriate seismic performance factors (R, ΩO, Cd) for new archetypical building structural systems, the methodology defines acceptably low values of probability against collapse under maximum considered earthquake ground shaking.

Evaluation of Reliability of the Earthquake Resistant Building Provided by Means of the Analysis for Design-Basis Earthquake

The paper analyzes the reliability level realized through the method recommended by SP 14.13330.2014 (Seismic Building Design Code). The results of the probabilistic analysis of a 16-storeyed earthquake-resistant building in terms of the action of the seismic load correspondent to the design basis earthquake are given. The analysis was carried out on the basis of standard computational procedures of the FEM, computerized in modern software packages for analysis, which are used in design practice. The comparison of the analysis results of two building models was carried out, both with and without regard to foundation beds deformations.

Integrated geophysical-geological model for seismic local site response: the Caldes alpine slope case (Southern Alps, NE Italy)

We present the seismic local response analysis of an alpine slope based on an integrated geophysical and geological model. The studied site is located in Caldes, in the lower Val di Sole valley in the Trentino region, Southern Italian Alps. Caldes represents the typical alpine valley formed by glacial and fluvio-glacial processes characterized by complex geomorphological, lithological and tectonic settings. A detailed reconstruction of the valley slope geology (subsoil geometry and stratigraphy) was obtained using electrical tomography resistivity soundings, controlled source multi-channel analysis of surface waves, microtremor single station measurements, borehole investigations, and geotechnical analyses on undisturbed samples. The geological model was shaken with real accelerometric series to obtain 1D (linear equivalent approach) and 2D (finite element approach) local seismic responses. The results, considering the uncertainties of the geophysical measurements, show different seismic responses between 1D and 2D approaches due to relevant geometrical amplifications, with clearer variations in the 2D approach. The comparison of the results with the building code design spectra shows the limits of the simplified approaches, suggesting that detailed characterizations are necessary, especially for such populous alpine environments.