Investigation of Deformation-Based Damage Limits of RC Columns for Different Seismic Codes

The seismic performance of reinforced-concrete columns is related to the expected damage limits under seismic loads and how this damage relates to safety of the structure. In order to assess the performance of reinforced-concrete columns under seismic loads, performance-based deformation and damage limits are proposed by the seismic codes. Adequacy of the deformation and damage limit levels given in the codes such as Seismic Evaluation and Retrofit of Existing Buildings Standard, ASCE/SEI-41 (2017) and Turkish Building Earthquake Code (2018) were evaluated by carrying out parametric studies for RC columns. Reinforced-concrete circular columns are designed in parametric studies to present the effects of various parameters such as concrete compressive strength, axial load levels and spiral reinforcement ratio on performance-based damage limits. Performance limits corresponding to each performance levels obtained by different seismic guidelines were compared. When the results obtained from the analyzes are examined, it has been observed that there are significantly different results in the cross-section damage limits values of ASCE/SEI-41 (2017) and TBEC (2018) regulation, which can change the performance level of the building. TBEC (2018) gives approximately 50% conservative limitations when they are compared with the ASCE/SEI-41 (2017) limitations. As a result, TBDY (2018) seems to offer safer and ductile solutions than ASCE ASCE/SEI-41 (2017).

Seismic Behavior of a Class of Mixed Reinforced Concrete-Steel Buildings Subjected to Near-Fault Motions

This paper investigates the seismic behavior of a class of mixed reinforced concrete­–­steel buildings. In particular, mixed buildings constructed by r/c (reinforced concrete) at their lower story(ies) and structural steel at their upper story(ies) are studied from the viewpoint of their wide application in engineering praxis. The need to investigate the seismic behavior for this type of mixed buildings arises from the fact that the existent literature is small and that modern seismic codes do not offer specific seismic design recommendations for them. To study the seismic behavior of mixed r/c-steel buildings, a 3-D numerical model is employed and five realistic r/c-steel mixed buildings are simulated. Two cases of the support condition, i.e., fixed or pinned, of the lowest steel story to the upper r/c one are examined. The r/c and steel parts of the mixed buildings are initially designed as separate structures by making use of the relevant seismic design guidelines of Eurocode 8, and then the seismic response of these buildings is computed through non-linear time-history analyses. The special category of near-fault seismic motions is selected in these time-history analyses to force the mixed r/c-steel buildings under study to exhibit a strong non-linear response. Seismic response indices in terms of inter-story drift ratio, residual inter-story drift ratio and peak floor absolute accelerations are computed. The maximum values of these indices are discussed by comparing the two aforementioned kinds of support conditions and checking the satisfaction of specific seismic performance limits. Conclusions regarding the expected seismic behavior of mixed r/c-steel buildings under near-fault seismic motions are drawn. Finally, the need to introduce specific design recommendations for mixed r/c-steel buildings in modern seismic codes is stressed.

Risk-adjusted Design Basis Earthquake’s Adequacy for use in Seismic Design Codes

In most buildings’ seismic design codes design basis peak ground acceleration (PGADBE) is provided by employing a uniform-hazard approach. However, a new trend in updating seismic codes is to adopt a risk-informed method to estimate the PGADBE so-called risk-adjusted design basis peak ground acceleration (PGARDBE). An attempt is made here to examine the adequacy of the PGARDBE to fulfill the assumptions made in seismic codes for converting the maximum considered earthquake’s (MCE) intensity to PGADBE. To this end, the performance of regular intermediate steel moment frames (IMF) is assessed in terms of collapse margin (CMR) and residual drift ratios in the event of MCE and design basis earthquake (DBE), respectively. The PGARDBEs are computed for Karaj County, Iran. A set of 96 index archetypes of regular IMF are designed considering four design parameters, which include the number of stories (2, 3, 6, 9, 12, and 15), span lengths (4 and 8 meters), occupancies (residential and commercial), and seismic demands (0.15, 0.25, 0.35 and 0.45g). The PGADBE prescribed by Standard No. 2800 for Karaj neither meets the assumed acceptance criteria nor stands on the safe side. Meanwhile, PGARDBE fulfills the acceptance criteria but does not necessarily satisfy the implicit assumption made in codes that the code-conforming buildings have at least a CMR of 1.5 if the MCE occurs. This emphasizes that the PGARDBE should not be used without examining the CMR fulfillment. The results recommend that a lower limit need to be set on PGARDBEs, which is found to be 0.35g for Karaj. Outcomes also reveal that the code-conforming buildings designed with the proposed PGARDBE can fulfill both repairability and life safety performances at the DBE and MCE, respectively. These buildings also have a high chance to be even considered as repairable ones at the seismic demand of MCE. Furthermore, regardless of the employed method for estimating PGADBE, various relationships between design parameters with different performance indicators such as CMR, residual drift ratio, ductility demand, imposed drift ratio, and building’s normalized weight are presented. These relationships can be used to evaluate the buildings’ safety factor against collapse and repairability, justification of using IMF in regions with high seismicity, level of structural and nonstructural damage as well as the economic consequence of changes in PGADBE. The presented relationships provide a multi-criteria decision-making tool to decide on the optimum PGADBE leading to an affordable alternative and tolerable damage.

Empirical assessment of seismic design hazard’s exceedance area

Design ground motion intensities determine the actions for which structures are checked, in the conventional approach of seismic codes, not to fail the target performances. On the other hand, due to inherent characteristics of probabilistic seismic hazard analysis (PSHA), it is expected that site-specific design intensity based on PSHA is exceeded in the epicentral area of moderate-to-high magnitude earthquakes. In the context of regional seismic loss assessment and of the evolution of seismic codes from the regulator perspective, it is useful to gather insights about the extent of the zone around the earthquake source where code-conforming structures are expected to be systematically exposed to seismic actions larger than those accounted for in design. To assess such areal extent based on empirical evidence is the scope of the study presented in the paper. To this aim, peak ground acceleration ShakeMap data for Italian earthquakes from 2008 to 2020 were compared to the current design intensities in the same areas for which the maps are available. This allowed, first, to develop simple semi-empirical models of the exceedance area versus the magnitude of the earthquakes. Second, it allowed to model the probability that an earthquake of given magnitude causes exceedance of the design intensity via logistic regressions. Coupling the first and second class of models provides an approximation of the expected exceedance (logarithmic) area upon occurrence of an earthquake of given magnitude. Such an area can be of several thousand square kilometers for earthquakes occurring relatively frequently in countries such as Italy.

Reconciling Architectural Design with Seismic Codes

Seismic codes include strict requirements for the design and construction of mid-rise reinforced concrete residential buildings. These requirements call for the symmetric and regular arrangement of the structural system, increased cross-sections for columns, and the introduction of shear walls to counteract the effects of lateral seismic loads. It is challenging for architects to reconcile the demands of these codes with the spatial arrangement and commercial appeal of their designs. This study argues that such reconciliation is possible through an architectural analysis. First, the effectiveness of applying the seismic design principles required by the codes is demonstrated with the comparative analysis of two finite element models. Then three pairs of architectural models, representing the most common floor plan arrangements for such buildings in Turkey, are architecturally analyzed before and after the application of seismic design principles in terms of floor area and access to view. The results demonstrate that within the context defined by the methodology of this study, considerable seismic achievement can be achieved in mid-rise reinforced concrete residential buildings by the application of relatively few, basic design features by the architects.

A study on earthquake performances of reinforced concrete buildings with various number of stories

Seismic codes generally require that the Equivalent Seismic Load Method or the Modal Response Spectrum Method is adopted in the design of buildings. In the equivalent seismic load method, the equivalent seismic static force applied to the building is determined depending on the seismicity of the region where the building is located, the usage class of the building, the fundamental period of the building and the building mass. Later, this equivalent seismic load is reduced by the seismic load reduction factor to take into account the increase in the capacity of the system and the decrease in the seismic demand due to the nonlinear and inelastic behavior of the system, i.e., by accepting limited inelastic deformations in the building subjected to the design earthquake. Then, structural system of the building is analyzed under the reduced seismic forces in addition to the vertical loads by using the load combinations given in the design codes. The process is completed by designing the sections and the structural elements of the building. Similar processes can be implemented by using the modal response spectrum method. The difference between these two methods is consideration of the higher modes of the building instead of the first mode only and the use of the modal masses of the building for each mode, instead of the total mass of the building. In the latter method, the contributions of the higher mode are combined by using specific superposition rules. The codes assume that the structural systems designed in this way will exhibit the almost same level of inelastic deformation, i.e., the controlled damage state, regardless of the building parameters, such as the number of stories. In this study, an attempt is made to investigate the validity of this implicit acceptance. For this purpose, the buildings with a various number of stories are designed by satisfying the bare minimum requirements of the code only, as much as possible. The seismic behavior and the lateral load capacity of these buildings are examined by the static and dynamic nonlinear analyses. The ratio of the nonlinear load capacity to the reduced equivalent seismic load is evaluated depending on the number of the stories of the buildings. The results which are presented in detail yield that the buildings with a low number of stories have relatively larger nonlinear lateral load capacity-to-the reduced elastic seismic load ratio, which is not compatible with the general implicit assumption made in the seismic codes.

Comparative Study of Indonesian Spectra Response Parameters for Buildings According To 2012 and 2019 Seismic Codes

The Indonesian government has determined a new seismic code for structural design of buildings and non-buildings, namely SNI 1726:2019. This new code is a revision of the previous code of 2012. The fundamental difference between the two seismic codes of 2012 and 2019 is in the earthquake hazard map (EHM) that was used. 2012 seismic code uses the EHM-2010, while 2019 seismic code uses the EHM-2017. The EHM-2017 has been updated by revising a data of subduction parameters and updating the number of active faults from 81 to 251. This revision has an impact on increasing the spectral value of SS and S1 which is a parameter that must be reviewed in structural planning. This study investigated the seismicity status of 34 cities in Indonesia by comparing the values of the spectra response parameters (SDS and SD1) according to seismic code of 2012 and 2019. This study found that the SDS and SD1 value from 2012 to 2019 increased in 15 cities but decreased or remained in 19 other cities. The cities that experienced an increase of SDS and SD1 values were Bandar Lampung, Banjarmasin, Bengkulu, Gorontalo, Jayapura, Manokrawi, Medan, Palembang, Palu, Pangkal Pinang, Pontianak, Serang, Surabaya, Tanjung Selor, and Yogyakarta. It seems that the vulnerability assessment of the existing building in the 15 cities must be done to estimate their capacity under earthquake load designed by 2019 Seismic Code. Overall, Jayapura city has the highest of SDS and SD1 values in 2019 compared to the other cities.

Evolution of seismic design codes of highway bridges in Chile

Chile, as a country with a long history of strong seismicity, has a record of both a constant upgrading of its seismic design codes and structural systems, particularly for bridges, as a result of major earthquakes. Recent earthquakes in Chile have produced extensive damage to highway bridges, such as deck collapses, large transverse residual displacements, yielding and failure of shear keys, and unseating of the main girders, demonstrating that bridges are highly vulnerable structures. Much of this damage can be attributed to construction problems and poor detailing guidelines in design codes. After the 2010 Maule earthquake, new structural design criteria were incorporated for the seismic design of bridges in Chile. The most significant change was that a site coefficient was included for the estimation of the seismic design forces in the shear keys, seismic bars, and diaphragms. This article first traces the historical development of earthquakes and construction systems in Chile to provide a context for the evolution of Chilean seismic codes. It then describes the seismic performance of highway bridges during the 2010 Maule earthquake, including the description of the main failure modes observed in bridges. Finally, this article provides a comparison of the Chilean bridge seismic code against the Japanese and United States codes, considering that these codes have a great influence on the seismic codes for Chilean bridges. The article demonstrates that bridge design and construction practices in Chile have evolved substantially in their requirements for the analysis and design of structural elements, such as in the definition of the seismic hazard to be considered, tending toward more conservative approaches in an effort to improve structural performance and reliability for Chilean bridges.

Assessment on earthquake resistance spectral design load criteria for buildings and infrastructures in Indonesia

General assessment on earthquake resistance spectral design load criteria for buildings and infrastructures associated with the recent development of Indonesian seismic hazard maps is presented in this paper. The assessment is directed toward general identification of their associated risks for input to policy formulation of disaster risk reduction management plans or strategies. Indonesian seismic hazard maps haveevolved for the last three decades. This is originated from an early development map before 2002, where a seismic hazard map particularly for buildings (1983) was developed adopting the early process of probabilisticseismic hazard analysis (PSHA) for 200 years return period (RP). Further, a 2002 version seismic hazard maphas been developed in the form of peak ground acceleration (PGA) for 500 years RP. Spectral design criteriafor buildings and bridges have been later developed by updating PSHA involving new seismic source zones, ground-motion predictive equations, and various earthquake RP, accommodating seismic codes for buildings(2500 years RP), for bridges (1000 years RP) and dams involving various RP up to 10,000 years RP correspond to its design level. The spectral accelerations also have included PGA, short (0.2s) period, and 1-s period. The latest update hazard maps (2017) have been developed and adopted for seismic codes for buildings, bridges, dams, and other related infrastructures. The increase in spectral design load criteria is identified to assess the general risk of existing constructions, considering the results of several recent building damage surveys. Adoption of new seismic codes based on the most recent hazard maps along with its enforcement is expected to contribute to seismic disaster risk reduction in Indonesia.