Probability of Failures of Strong Column-Weak Beam Moment Resisting Reinforced Concrete Framed Structures Subjected to Seismic Ground Motions

• Main Author: HENDRA PRAYOGA - NIM: 25016022, MADE
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/28696
• Institution: Institut Teknologi Bandung

<p align="justify">Indonesia is an earthquake prone areas. Major earthquakes that have hit Indonesia include Aceh Earthquake in 2004 (9.3 SR), Nias Earthquake in 2005 (8.7 SR), Bengkulu Earthquake in 2007 (7.9 SR) and Lombok Earthquake in 2018 (7 SR). So a research study on the vulnerability level of building at an earthquake intensity value and the risk level of building due to an earthquake needs to be conducted. The vulnerability level of building can be predicted by the development of fragility curves. Fragility curves indicate the probability of a structure achieving a certain performance level or damage level at a certain PGA (Peak Ground Acceleration) value. While the risk level of structure due to an earthquake is presented through a Pf (Probability of Failure) value which is a convolution of the median structure fragility curve with the median hazard curve for a particular site. The median curve is associated with a 50 % confidence level (Q). The hazard curve shows the probability of exceeding certain PGA values on a site based on seismic characteristics around the site. <br /> <br /> <br /> In this study, fragility curves were developed based on Pushover Analysis (NSP) at performance point and Nonlinear Time History Analysis (NLTHA) for the performance level of FY (First Yield), IO (Immediate Occupancy), LS (Life Safety) and CP (Collapse Prevention ). Two structural models are used namely hypothetical structure and realistic structure. Hypothetical structure using materials, cross-sectional dimensions and reinforcement based on the research study of Diagonal Reinforcement Performance at Plastic Hinge Region of Beam in Energy Dissipation (Samsuardi Batubara, 2003). While the realistic structure is designed based on The Indonesian Building Code (SNI 2847:2013) with an earthquake resisting system namely SMF (Special Moment Resisting Frame) and OMF+ (Modified Ordinary Moment Resisting Frame). In addition to the OMF+ structure, reinforcement detailing and transversal reinforcement is ensured to be sufficient to prevent premature failure due to shear and is designed to meet the strong column-weak beam requirement. All structures consist of four spans in the short direction and six spans in the long direction of the structure. The length of each span is 3.6 m for hypothetical structure while for realistic structures are 6 m (short direction of the structure) and 5 m (long direction of the structure). All structures consist of eight floors with a height of each floor is 3 m for hypothetical structure and for realistic structures that are 4 m on the ground floor and 3.5 m for the floors above. For realistic structures also developed fragility curves and risk level if soft story mechanism occurs. <br /> <br /> <br /> After analyzing NSP and NLTHA on the design PGA, the structures have not reached collapse. Plastic hinges that are formed on beams and columns are at the IO to LS performance level. Plastic hinges on columns are only formed at the base of the ground floor column so that the provision of strong column-weak beam (&#931;Mnc &#8805; (1.2)Mnb) is adequate. The collapse criteria in this study is that 95 % of beam potential plastic hinges in the weak axis direction of the structure reach the CP performance level. In the weak axis direction, the structure is driven by a major earthquake. The structure must be able to achieve the performance level of FY, IO, LS and CP safely. In general, the performance level of CP is achieved in PGA which is greater than the design PGA. For PGA values greater than the design PGA, the provision of &#931;Mnc &#8805; (1.2)Mnb is inadequate because plastic hinges on columns occur in the ground and middle columns of the structure. This situation causes story mechanism so that the column needs to be strengthened. After the column is strengthened, the ratio of nominal flexural strength of column to beam &#931;Mnc / &#931;Mnb) is 3.6. The ratio is in accordance with the minimum ratio based on the research study of Seismic Collapse Safety of Reinforced Concrete Buildings (Haselton et al., 2011), namely 3. The Pf value of all strengthened structures is smaller than the performance goal of 2 x 10-4 (SNI 1726: 2012). The hypothetical structure is the most robust structure against an earthquake with the smallest Pf CP value of 1.796 x 10-6. This value is 111 times smaller than the performance goal. Pf CP of OMF+ structure is 2.184 x 10-5, the value is 4 times smaller than the Pf CP value of SMF structure which is 9.387 x 10-5. So that structure with smaller value of response modification factor (R) or ductility (&#956;) will have smaller Pf value. Pf CP value of SMF structure is 2 times smaller than the performance goal while for OMF+ structure reaches 9 times. While the Pf CP value of non-strengthened OMF (Ordinary Moment Resisting Frame) structure is 2.758 x 10-4, the value is 1.4 times greater than the performance goal. So the OMF structure is vulnerable to earthquakes due to premature failure due to shear. Performance point which is demand based on NSP is associated with the IO performance level based on NLTHA. So the Pf value of NSP is correlated with the Pf value of the IO performance level based on NLTHA. The strengthened structure of SMF and OMF+ is not vulnerable to soft story mechanism, because Pf values for structures with soft story mechanism are smaller than performance goal. Soft story mechanism on the ground floor is more likely than on the floors above, because it occurs in the smallest PGA.<p align="justify"> <br />