Evaluation of Seismic Response Modification Factor (R) for Moderate-Rise RC Buildings with Vertical Irregular Configurations

Most international design codes consider the nonlinear seismic performance of a structure by the concept of reduction/modification factor (R). Then, an elastic static force-based method can be normally used for seismic design to create earthquake resistant RC buildings. The response modification factor (R) is sensitive to many aspects such as overall ductility, over-strength, damping, and redundancy levels. Indeed, these factors are severely affected by geometric irregularity of the structural system. So, R-value does not become a constant number for the all types of structures with the same lateral load resisting system, as many standard codes noted. It depends on types, combination, and degrees of geometric vertical irregularity. This research assesses the actual values of R for regular and familiar vertical irregularity cases in RC buildings with moment-resisting frames (MRF) systems. Also, it takes into account the reduction percent that may occurs in R-value due to these studied vertical irregularities. The vertical irregularity cases, such as set-back and soft story, are essentially needed to be studied greater than ever due to the wide propagation of these types of buildings in Egypt, recently. In addition, the potential analytical methods that may be used to calculate R-value in comparison with Egyptian code’s value. Nonlinear static pushover analysis is carried out using ETABS via three-dimensional numerical models. The findings prove that vertical irregular models have poor seismic capacities, in comparison with regular one, due to their sudden change in lateral stiffness than that with regular aspect. So, the response modification factor (R) must be re-calculated or even scaled-down before design stage with 15% and 25% for single and combined vertical irregularity, respectively. In addition, this investigation derives a vital equation between R values with vertical irregularity ratios in each studied model. This equation shall be a guide for seismic design codes, structural design engineers, and researchers. Accordingly, the response modification factor R does not become a fixed value regardless vertical irregularity aspects of the buildings, but it has a variable value that depend on their inelastic seismic performance of the lateral load resisting systems.

EVALUASI KINERJA STRUKTUR DUAL SYSTEM DENGAN BELT TRUSS

In structural engineering applications, the limit of building deflection or interstory drift is an important issue. In high-rise buildings that are more than or equal to 60 floors in the current era, systems are used in the structure of the building. The function of the Belt Truss is to reduce the deflection that occurs in the building by converting the building's overturning moment into the axial force of the exterior column. The Belt Truss structure itself can use reinforced concrete structures and steel structures. Because the Belt Truss structure is an innovation in the world of structural engineering, the parameter values for earthquake loads are not listed in the applicable Building Planning Standards. The standard for earthquake-resistant building regulations requires the parameters of Response Modification Factor (R), Overstrength Factor (Ωo), and Deflection Magnification (Cd) for determining earthquake loads. Because the parameters on the Belt Truss structure are not listed in the Standard for Earthquake Resistant Building Regulations, a study of the earthquake load parameters on the Belt Truss structure was carried out. The method used in this research is a literature study using Pushover Load Analysis according to ATC - 40 and FEMA 356. Keywords: Belt Truss, Dual System; ATC – 40; FEMA 356; Response Modification Factor (R); Overstrength Factor (Ωo); and Deflection Magnification (Cd) AbstrakDalam aplikasi rekayasa struktur gedung, batasan defleksi bangunan atau interstory drift adalah masalah penting. Pada bangunan tinggi yang lebih dari atau sama dengan 60 lantai pada era sekarang sudah menggunakan sistem pada struktur bangunan tersebut. Fungsi dari Belt Truss tersebut berguna untuk mengurangi defleksi yang terjadi pada bangunan dengan mengkonvesi momen guling bangunan menjadi gaya aksial kolom eksterior. Struktur Belt Truss sendiri materialnya bisa menggunakan struktur beton bertulang dan struktur baja. Karena struktur Belt Truss merupakan inovasi pada dunia rekayasa struktur, maka nilai parameter beban gempa tidak tercantum pada Standar Peraturan Perencanaan Bangunan yang berlaku. Standart Peraturan Bangunan tahan gempa diperlukan parameter – parameter Faktor Modifikasi Respon (R), Faktor Kuat Lebih (Ωo), dan Perbesaran Defleksi (Cd) untuk penentuan beban gempa. Dikarenakan parameter pada struktur Belt Truss tidak tercantum pada Standar Peraturan Bangunan Tahan Gempa, maka dilakukan penelitian parameter-parameter beban gempa pada struktur Belt Truss tersebut. Metode yang digunakan dalam penelitian ini adalah studi literatur dengan menggunakan analisa Beban Dorong Pushover Analysis sesuai ATC - 40 dan FEMA 356.

Evaluation of NSP and MPA Methods to Optimize Special Truss Moment Frames (STMF) Using Island Genetic Algorithm

The purpose of the present study is to evaluate the Pushover (NSP) and Modal Pushover (MPA) analysis methods in optimizing Special Truss Moment Frames (STMF) using island genetic algorithm. For this purpose, the optimization program is written and developed in Matlab software, and OpenSees software is used for structural analysis. The design variables of truss arrangement, cross section of members, truss height values and length of special zone of truss moment frame are considered. The constraints of the optimization problem are based on the rules and restrictions of AISC341-16. Case studies were performed on five frames of 3, 6, 9, 12 and 15 stories with a story height of 3 meters and span length of 18 meters with the aim of minimizing weight and maximizing the response modification factor. The results of these analyses are compared with nonlinear dynamic time history analyses as the most accurate method available, which could be used to finally identify and introduce the most efficient method in these structures. The MPA method was able to show better performance than the NSP method in estimating the maximum response of the structure. Despite the excellent performance of this method, Evaluation of numerical results of this study indicates the non-economic nature of MPA method for low-rise structures, and the acceptable efficiency of this method for medium-height to high-rise structures.

The Response Modification Factor for Seismic Design of Integral Abutment Bridges

The response modification factor (R factor) is a crucial parameter for calculating the design seismic forces applied to a bridge structure. This factor considers the nonlinear performance of bridges during strong ground motions. Conventional bridge structures rely on the substructure components to resist earthquake forces. Accordingly, there are R factors available in the design codes based on the type of bridge substructure system. Lateral load resisting system of Integral Abutment Bridges (IABs) in the longitudinal direction is more complex than ordinary bridges. It involves the contributions from soils behind the abutments and soil/structure interaction (SSI) in addition to existing rigid connection between the superstructure and abutments. There is no R factor available in any design code throughout the world for IABs in the longitudinal direction that considers all these parameters. In this research, the Federal Emergency Management Agency publication FEMA P695 methodology has been applied to estimate the R factor for IABs. It is found that 3.5 could be a safe and valid R factor in the longitudinal direction for seismic design of such bridges.

RESEARCH INTO THE DEVELOPMENT OF A RESPONSE MODIFICATION FACTOR FOR DIAGRID STRUCTURES

The diagrid structure system has recently gained popularity as an effective structural system for high rise buildings. The effectiveness of the system relies on the truss action developed by the perimeter diagrid system to resist lateral loads. In active seismic zones, ductile performance of the lateral resisting system is highly desired to dissipate energy developed in the structure from the ground shaking. In this study, the seismic performance of the diagrid system is investigated. Non-linear static pushover analysis followed by non-linear dynamic analysis were conducted to study the inelastic behaviour of diagrid systems. Through methods of analysis, the response modification factor of the modelled system was calculated. The results indicate that the reserve strength of a diagrid system is comparable to and often greater than that of many other lateral structure systems, such as steel special truss moment resisting frames and other structural systems as prescribed by the ASCE 7-10.

Effect of ‘X’ Type Bracing on Response Modification Factor for R.C. Building with Special Shaped Column Cross Sections

Earthquake is the most destructive natural hazard in the world. While designing any earthquake resistant structure, actual forces developed are much higher than designed forces. Therefore, to get design lateral force, the actual base shear force should be reduced by the factor known as response modification factor(R). Response modification factor plays vital role in seismic design of structures. Components of response modification factor (R) are ductility factor, over strength factor, redundancy factor and damping factor. Generally, value of response modification factor is adopted from seismic design codes of developed countries such as Europe, United States and India. Column is important part of Reinforced concrete building as overall load is transferred through column. Not only from aesthetical point of view, but also from structural aspect special shaped columns performs better than rectangular columns. So this study aims at calculating components of response modification factor(R) for column cross section with special shapes (L, T, +) for ‘X’ type bracing. In this study total 16 models of different number of storeys i.e. 5,10 are analysed using Pushover analysis for different seismic zones. The study also involves comparison of response modification factor (R) for structures designed with Indian code IS1893:2016(Part1) and American code ASCE 7-16.