Egyptian Code Seismic Load Design Provisions for Moment Resisting Frames
Abstract
The occurrence of any seismic activity can impact the robustness of the structure as well as the human lives, the Egyptian code of practice of seismic loads is mainly concerned about maintaining the safety and the structural integrity of the structures. In this study an estimation of the strength reduction factor of the different seismic zones in Egypt is to be implemented. Moreover, the probabilistic seismic hazard map of Egypt is also evaluated to test the soundness of the currently used seismic zones map in Egypt.
1 Introduction
According to the Egyptian code of practice Egypt is to be categorized into 6 seismic zones (Zone 1, 2, 3, 4, 5A and 5B). The main objective of this paper is to study the variation of the response modification factor determined by the Egyptian code of practice due to the change in seismic zones, 2 analytical models are to be implemented via SAP 2000 software using pushover nonlinear static analysis on a 2 storey building and 3 storey building respectively.
The analysis predominantly depend on the application of the base shear generated according to the Egyptian code of practice for each seismic zone on the 2 storey 2D frame and the 3 storey 2D frame respectively. Moreover, applying the pushover analysis to know the capacity of the structure.
2 Response Modification Factor
 \( {\text{R}}_{\upmu} {\text{R}}_{\upmu} : \)

Ductility reduction factor.
 \( {\text{R}}_{\text{s}} {\text{R}}_{\text{s}} : \)

Overstrength factor.
 \( {\text{R}}_{\upxi} {\text{R}}_{\upxi} : \)

Damping factor.
The three factors \( {\text{R}}_{\upmu} {\text{R}}_{\upmu} \), \( {\text{R}}_{\text{s}} {\text{R}}_{\text{s}} \), and \( {\text{R}}_{\upxi} \) take account of many characteristics of the structure energy absorption and dissipation through undergoing plastic deformations, redistribution of internal forces in the inelastic range, and damping of the structure through the supplemental viscous damping devices.
2.1 Overstrength Factor (Rs)
2.2 Ductility Reduction Factor (Rµ)
This factor depends on a characteristic of the structure that is called the Ductility factor μ, which defined as the ability of the structure to undergo large plastic deformations without significant loss of strength. It can be mathematically presented as the ratio between the maximum ultimate deformation Δu at an assumed collapse point to the yield deformation Δy.
3 Validation Process
An experimentally obtained pushover curves of a 0.25 size RC frame models from (Paul et al. 2011) with and without infill wall and steel bracing have been used to calibrate the nonlinear analytical model of the frame. The pushover testing has been carried out on three nonductile frame models namely bare frame (BF), infilled frame (INF) and a steel braced (SBF) frame under quasistatic condition. The nonlinear analytical model is further extending for the seismic evaluation and retrofitting of a 4storied 2D frames using infill wall and steel bracing. In this context; firstly a 4storied 2D RC frame structure has been analyzed and designed using different versions of IS: 456 and IS: 1893. Reevaluation of these frames has been carried out to with masonry infill and steel bracing as retrofitting scheme using pushover analysis. The different pushover parameters of the frames before and after retrofitting have been compared.
4 Analytical Model
The undermentioned 2D frames are designed according to the Egyptian code of practice ECP201and ECP203, in order to calculate gravity and seismic loads on the following buildings in given seismic zones accordingly.
The beams’ dimensions are to be 300 mm * 650 mm and the columns’ dimensions are to be 600 mm * 600 mm in all the moment resisting frames (2 storey and 3 storey). The materials used in the design of systems members are concrete (confined and unconfined), which has a unit weight of 2.5 t/m^{3}, a characteristic strength of 30 MPa, and Poisson’s ratio of 0.20. Yield strength of 360 MPa, and ultimate strength of 520 MPa (high grade steel).
For a given 2D frame the Live load = 3000 N, thickness of slab = 0.2 m, Floor covering = 2000 N.
5 Results
The 2 storey frame model plan dimensions are 10 m × 10 m as shown in Fig. 2 resting on dense sand soil which is to be located in seismic zones 1, 2, 3, 4, 5A and 5B. As for the 3 storey frame model the plan dimensions are 15 m × 15 m as shown also in Fig. 2 resting on dense sand soil which is also to be located in seismic zones 1, 2, 3, 4, 5A and 5B respectively. While the elevations of both frames are illustrated in Fig. 3, consisting of a storey height of 3 m and a fixed end supports.
Base shear for 2 storey and 3 storey buildings in different seismic zones in Egypt.
Fb (Base shear according to ECP) for 2 storey building in KN  Fb (Base shear according to ECP) for 3 storey building in KN  

Zone 1  84.8  161.339 
Zone 2  106  201.673 
Zone 3  127.2  242.008 
Zone 4  169.6  322.667 
Zone 5A  212  403.346 
Zone 5B  254.5  484.016 
From Table 1 it is noticed that the magnitude of the base shear described by the Egyptian code increases radically for the same structure through the different seismic zones, for the 2 storey and the 3 storey frame the base shear gradually increase from seismic zone 1 (low seismicity) to zone 5B (higher seismicity) as shown in Fig. 27 according to Egyptian seismic map.
For the 2 storey frame the base shear increases by 201% from zone 1 to zone 5B, and for the 3 storey frame the base shear increases also by 200%, which is predicted to have a direct influence on the strength reduction factor (R).
Response modification factor for 2 storey building in different seismic zones in Egypt.
2 storey moment resisting frame  

Vy (KN)  Vd (KN)  ∆u (mm)  ∆y (mm)  Rµ  Ω  R  
Zone 1  102  84.8  120  28  4.285  1.202  5.154 
Zone 2  118  106  119  26  4.576  1.113  5.095 
Zone 3  140  127.2  120  26  4.615  1.100  5.079 
Zone 4  180  169.6  120  26  4.615  1.061  4.898 
Zone 5A  257  212  120  30  4.001  1.212  4.849 
Zone 5B  285  254.5  120  28  4.285  1.119  4.799 
Average =  4.979 
Response modification factor for 3 storey building in different seismic zones in Egypt.
3 storey moment resisting frame  

Vy (KN)  Vd (KN)  ∆u (mm)  ∆y (mm)  Rµ  Ω  R  
Zone 1  193  161.339  180  42  4.285  1.196  5.126 
Zone 2  228  201.673  180  40  4.500  1.130  5.087 
Zone 3  282  242.008  180  42  4.285  1.165  4.993 
Zone 4  353  322.667  180  41  4.390  1.094  4.802 
Zone 5A  420  403.346  180  40  4.500  1.041  4.685 
Zone 5B  499  484.016  180  40  4.500  1.030  4.639 
Average =  4.889 
In the case of the 2 storey frame, the calculated strength reduction factor has decreased by 3.3% from zone 1 to zone 5B, correspondingly the 3 storey frame’ strength reduction factor has decreased similarly by 8% from zone 1 to zone 5 B.
The static pushover curve of the 2 storey frame in seismic zone 1 has a maximum base shear (Vy) from Table 2 of 84800 N while in seismic zone 5B has Vy of 254500 N which has also incremented by 171.56%. Which leads us to the conclusion that the Response modification factor would be directly impacted due to the change in seismic zones, as per noticed in Table 2 as well the response modification factor (R) for the 2 storey frame in seismic zone 1 is 6.71 and in seismic zone 5B is 2.93 which has exponentially decreased by 56.33%, as for the 3 storey frame the response modification factor (R) from Table 3 in seismic zone 1 is 6.3 while in seismic zone 5b is 2.07 which has similarly decreased by 67.14%.
Correspondingly it has been noticed that the Response modification factor for the same structure decreases gradually from seismic zone 1 to seismic zone 5B, taking into consideration that the Response modification factor for the 2 storey frame is higher than the response modification factor of the 3 storey frame in the same seismic zone as shown in Fig. 6 which is rational due to the change in the ductility factor (Rµ) between each structure.
The ductility factor (Rµ) for the 2 storey frame in seismic zone 1 is 5.7 from Table 2, while for the 3 storey frame in the same seismic zone is 5.53 from Table 3.
6 Conclusions
A total number of 12 2D moment resisting frames has been analyzed via SAP 2000 software to comply with the provisions and considerations of the Egyptian seismic code in the 6 different seismic zones in Egypt.
As per noticed the response modification factor decreases with respect to the seismic zone, for seismic zone 1 has higher response modification factor than seismic zone 5B for the same structure. Which indicates that the more the seismic hazard within the seismic zone the less the response modification factor would be.
Also the 2 storey 2D frame has higher response modification factor than the 3 storey 2D frame, in that regard according to the design based on the Egyptian seismic code the base shear force increases noticeably from the 2 storey frame than 3 storey frame within in the same seismic zone.
The observations mentioned above calls for the seismic Egyptian provision code to take into consideration the variation of the response modification factor. Correspondingly the moment resisting frames with high response modification factor (R) do perform better under the application of lateral loads, with a less likely of a brittle failure than the frames with less (R).
Notes
Acknowledgement
I would like to express my deepest gratitude and appreciation for the Civil Engineering program at the German University in Cairo for providing me with the support and the facilities throughout my work on this research.
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