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- ItemEFFECT OF SETBACK ON THE ELASTIC DYNAMIC RESPONSE OF REINFORCED CONCRETE FRAMED STRUCTURES(2023-01-03) Aseel Jamal Fareed BadranBackground: The collapse due to a seismic load typically starts at locations of the weakness of the structural system in the building. The weaknesses often occur due to a discontinuity in mass, strength, or stiffness between two adjacent floors. A well-known type of vertical geometric irregularity in structures is a setback, defined as a sudden decrease in the building's lateral dimension at a certain height. Problem Statement: The ASCE 7:16 code sets limitations on the Linear Equivalent Static method (LES), where it does not permit the use of this method for some types of irregularity, including setback irregularity, which are located in seismic design category (SDC) D, E and F. On the other hand, the LES method can be used in SDC B and C without restrictions. The code permits using the Modal Response Spectrum (MRS) and the Time History Analysis (THA) for all buildings without limitations on the SDC. Objectives: This study examines the effect of a setback on the elastic seismic response parameters of reinforced concrete framed structures, such as the fundamental period, the seismic base shear, the inter-story distribution of shear forces, and story drift. Finally, this study examines the solution to the problem of the code restrictions on the use of the LES method. Methodology: Buildings with Perimeter masonry walls with different setback ratios at different levels were analyzed using the commercial software ETABS 2016 according to the provisions of ACI318-14 and ASCE 7:16. The analysis was done using the LES method, MRS method, and THA method. The outcomes of the elastic response of the setback buildings were compared to similar buildings but without setbacks, in addition to comparing the results of the analysis methods used in this study. Conclusion: Based on the results, the vertical distribution of shear force from LES was modified depending on the THA method results. This modification allows the use of the LES method in various SDCs. Keywords: Linear Equivalent Static Analysis (LES); Modal Response Spectrum (MRS); Seismic Response; Setback structures; Time History Analysis (THA).
- ItemEFFECT OF HORIZONTAL COMPONENT OF EARTHQUAKE ON HANGED ROOFS LOADED WITH HEAVY WALLS(2022-05-17) Motaz Mohammad Ibrahim Abu AladasBackground: It can be clearly seen that most of today's buildings contain cantilevers, and in most cases these cantilevers are loaded by moderate to heavy masonry loads. The effect of earthquake components on the loaded cantilevers is not clearly described in the design codes, which is a research interest. The main objective of this research is to understand the behavior of cantilevers when subjected to a horizontal earthquake component under different conditions, since the codes do not give the necessary attention to the weakness of cantilevers and their effects on the vulnerability of structures. Methods: Some of the most sensitive properties of cantilevers were selected to study the behavior of cantilevers and their effects on the response of structures. The literature review included the investigation and collection of information on the most important factors affecting the behavior of cantilevers, such as direction, length, and loading of cantilevers. In order to study each of these parameters, a series of models with specific parameters were analyzed in the Extended 3D (Three Dimensional) Analysis of Building Systems (ETABS) software after being verified and adopted. Results: the results of the forces and stresses in the presence of masonry have an increase of 152% for axial forces and 13.4% for shear forces and bending moments due to the horizontal component of the earthquake. On the other hand the vertical earthquake component does not have an axial effect on the cantilevered sections and the effect of axial stress due to the horizontal earthquake component on the shear capacity of sections does not exceed 2% for beams and 1% for ribs. And critical cantilever length to successive span length can reach 22% in some cases. Conclusion: The research indicate that it’s recommended to avoid an irregular structure to minimize the inherent torsion. On the other hand, a regular structure, where the center of mass coincides with the center of stiffness, may have a torsional response in some cases. Research has also shown that the horizontal earthquake component does not cause a significant decrease in shear capacity and that the vertical earthquake component is not worse than the horizontal one. Keywords: loaded cantilever, torsional mode, horizontal earthquake component, vertical earthquake component, site seismicity.
- ItemEFFECT OF THE BUILDING ASPECT RATIO ON RESPONSE MODIFICATION FACTOR FOR REINFORCED CONCRETE MOMENT RESISTING FRAMES(2023-07-02) Dana Issam Abdul Kareem NassarAbstract The response modification factor (R) is one of the essential factors in seismic design and is used to define the nonlinear behavior of buildings during an earthquake. International codes such as IBC 2016 provide a constant value for “R” for a particular structural system. However, the value of "R" may change based on parameters including zone factor, soil site class, aspect ratio of the frame, column orientation, and type of slabs. This study investigates the effect of building aspect ratio on the value of "R". In addition, it checks if the values of the R factor recommended by the IBC-2016 code are conservative. A single cycle for calculating the R factor is applied by pushover analysis (nonlinear response analysis) to achieve this goal. It was applied to many 3-D intermediate moment-resisting frame systems with different aspect ratios as the key parameter and different seismic zone factors and sites as secondary parameters to determine the behavior of the frame with increasing lateral force until collapse. The researcher selected 30 cases with different aspect ratios, zone factors, site classes, and building plans. Then, the ETABS2016 program is used to design and analyze (elastic analysis) the 3-D frames as per previous code requirements. Finite element software (ABAQUS) performs the nonlinear analysis via incremental Elasto-Plastic analysis. The reinforced concrete elements are presented in the program as line elements. Afterwards, the Xtract program is used to evaluate the inelastic properties of the sections fed to ABAQUS for the frame analysis. The obtained results of "R" are compared to the values suggested by international codes (IBC 2016). The results demonstrate an influence of the aspect ratio, zone factor, and site class on the R factor. An equation was derived to calculate the R factor through the aspect ratio of the building and the seismicity of the region. Consequently, the computed values for the cases depending on the pushover curve are larger than or equal to those recommended by the IBC2016 code. So, the international code is conservative, in term of the total base shear, force because it considers the period of the building in the calculation of the R factor. However, further ductility investigation is needed as the required R values are higher than code ones. Keywords: Nonlinear static analysis; ABAQUS program; response modification factor
- ItemUSING ULTRA-HIGH PERFORMANCE CONCRETE FOR ELIMINATING SOFT AND WEAK STORY IRREGULARITIES IN SPECIAL REINFORCED CONCRETE MOMENT RESISTING FRAMED STRUCTURES(An Najah National University, 2022-02-27) Mohammad Sharawneh, AliMultistory buildings are common in Palestine and sometimes are built with a ground floor that has an open space or is higher than the rest floors for commercial purposes. Therefore, the soft and weak story irregularities may occur on the ground floor. This research aims to eliminate the soft or weak story irregularities in the design stage without affecting the architectural requirements by changing the columns material from normal strength concrete (NSC) to ultra-high performance concrete (UHPC) in the soft or weak story. To quantify the effect of the material switch from NSC to UHPC on the column strength and stiffness, a parametric study using sectional stress analysis is performed. Overall, 216 NSC and UHPC columns cross-sections are analyzed under the following parameters: axial load levels, longitudinal reinforcement ratio, cross-section width, and cross-section depth to width ratio. The effectiveness of using UHPC on the column stiffness is studied where the change in the flexural rigidity is represented using the ratio of the effective flexural rigidity (EIe) of UHPC columns to NSC columns. Also, the validity of cracking analysis modifiers of NSC columns is established for UHPC columns. The effectiveness of using UHPC on the column strength is investigated using the ratio of the moment capacity of the UHPC columns to NSC columns. After that, the adequacy of the column shear capacity is checked, and found that the lateral strength of the UHPC column is still controlled by the moment strength. Moreover, regression analysis is performed for the parametric study results to create equations that predict the increase in the sectional stiffness and strength of the columns. Finally, a 3D sway special moment-resisting framed building is used as a case study to confirm the sectional analysis results and to investigate the frame's overall behavior before and after using UHPC in the soft/weak story columns. The frame is designed according to ASCE7-16 and ACI318-19 and has both an extremely soft story and weak story irregularities on the ground floor. Nonlinear static analysis (pushover) is performed for the frame using SAP2000. The frame analysis results agree well with the parametric study results. In addition, the overall behavior of the frame is enhanced when the UHPC is used since the displacement and the plastic hinges do not concentrate on the soft/weak story. In summary, switching the columns material in the soft/weak story from NSC to UHPC can be safely used to eliminate the soft/weak stories irregularities at the design stage without changing the architectural or functional restriction.
- ItemSeismic Assessment of Public Schools in Palestine According to International Building Code IBC(جامعة النجاح الوطنية, 2019-07-22) Adas, Mohammad OmarIt is known that schools in countries need special requirements for implementation issues controlling all needs reaching the best way for safely use to all occupants. Moreover; schools -as they are core of communities- used as shelters in Severity circumstances like wars, damages …etc. Schools have a high degree of importance and focus on their physical status, which means the need to ensure their durability, sustainability and the integrity of all their components, as well as the global practice of using them as shelters in the event of natural disasters Human and various emergencies. The great importance of these facilities - schools - puts us in charge of community, ethics and professionalism beyond personal interests, and it is imperative in the field of engineering and construction design to ensure work to provide maximum care and safety, to stand these important facilities to all risks, for example, Seismic dangers. A great part of existing schools' structures in Palestine have been constructed using the same project details; with our concerning the seismic criteria including site conditions. In this research, we present an engineering scientific study that evaluates the topographic impact and the effect of its changes on seismic behavior and the difference in the design of public-school facilities in Palestine based on Time period of fundamental mode of structure according to codes of practice. Scientifically; It is proven that seismic behavior varies from region to region and from one structure to another according to many variables, mainly the nature of the soil on which the origin will be established. Hence, it is far from right to have the same seismic design for a number of schools located in several different places Terrain and seismic behavior. Different topographies directly affect seismic design factors, system considerations, importance of structure, and structural analysis methods. The study targeted a number of different designs of public schools in Palestine to collect statistical information about the nature of practice in previous years. The statistical data were used to create three school models in three different topographies (Jericho, Ramallah and Qalqilya). And to make the necessary recommendations based on Time period of fundamental mode of structure as a minimum in access to the safety of public schools within several construction systems of the same structure, and the results were obtained and a comprehensive overview of the best means and systems of the construction design of public schools in the occupied Palestinian territories. Several tools were used in local code-based analysis and evaluation, such as SAP program, and the results obtained were verified to ensure the reliability of the program and all its outputs. An interesting result has been found that puts the structural designer on the proper path of the safe structural design, within the necessary hypotheses that develop these structures from the structural aspects. The study also linked some design needs to the correct practice which means linking design to different implementation needs.