الفهرس 
LITERATURE REVIEWOnly 14 pages are availabe for public view
 |  | from | 342 |  |  |
| | | from | 342 | | |
Abstract
This research was performed to investigate the effect of foundation soil flexibility on the dynamic behavior of multi-story concrete buildings. A review of previous literature was undertaken to have a clear idea of the previous findings related. A technique for reinforced concrete (RC) structures considering soil modelling was developed and the experimental results of previous studies available in literature were verified using ABAQUS 6.14 software.
The main goal of this research was to study the effects of a number of parameters on the seismic capacity performance of multi-story buildings considering the soil-structure interaction. The following subjects are included in the work:
(I) Seismic capacity performance of Multi-story buildings considering fixed base in modelling (5, 10, 15 stories with basements).
(II) Amplification factors for the different soil types B, C & D using ground motion records (free field case and 5 stories with basements). The results have been compared with recommended values in ASCE7 and Eurocode8.
(III) Seismic capacity performance of Multi-story buildings considering SSI with different soil types B, C & D in modelling (5, 10, 15 stories with basements).
(IV) Seismic capacity performance of Multi-story buildings considering Irregularity in elevation.
The conclusions of the current research and recommendations for further work are presented.
6.2 CONCLUSIONS
A study was conducted to understand the influence of different parameters on the seismic capacity performance for frame and shear wall systems for RC structures. The following conclusions can be stated regarding the following points:
6.2.1 Modelling approach using ABAQUS program
Experimental static and dynamic results of individually tested reinforced concrete (RC) structures with and without SSI were used in order to verify modelling technique using ABAQUS program. The comparison between the experimental and analytical results showed a negligible error, consequently the ABAQUS analytical models could be considered to capture the real behaviour of the RC concrete structure considering soil structure interaction (SSI).
6.2.2 Seismic capacity performance of multi-story buildings considering fixed base in modelling
Three case studies (5, 10 & 15 stories) were analyzed to investigate Seismic capacity performance of Multi-story buildings (limited ductility) considering fixed base in modelling. The response modification factor (R) has been determined considering the effect of number of stories of the building. The following was noticed:
1. The results of Response modification factor, R, using both pushover static analysis and dynamic time history analysis are approximately having the same range
2. Increasing number of stories from five, ten to fifteen leads to:
- Increase time period, Ultimate and yield displacement
- Decrease ultimate, design base shear and response modification factor (R).
3. The response modification factor (R) for the three studied cases (5, 10 & 15 stories) are 7.06, 5.29 and 3.47 respectively.
4. The given value of R-factor at ECP-201(2012) equals 5.0 for limited ductility class of reinforced concrete dual system from moment resisting frames and shear walls structures is unconservative value as the actual value of R-factor is less than the given value.
6.2.3 Amplification factor for different types of soil considering different peak absolute accelerations
Analysis models were used to calculate amplification factors for the free field case using time history method (the ground motion records for Northridge 1994, Imperial valley 1940 & San Fernando 1994, PEER database and simulated ground motion records recommended by ECP 2012 for spectra types 1 & 2) considering different peak absolute accelerations (0.075g, 0.15g, 0.20g, 0.25g & 0.30g). The results illustrated that:
1. Changing the peak absolute acceleration from 0.075g to 0.15g, 0.2g, 0.25g & 0.3g leads to a significant change in amplification factor values which means that ECP & Eurocode shall consider peak absolute acceleration as an important parameter in amplification factor values, as considered in ASCE.
2. Increasing peak absolute acceleration leads to a decrease in amplification factor values for all considering soil types and ground motion records.
3. There is a significant difference for soil amplification factor especially at small intensity ground motions for ECP (which is similar to Eurocode 8) site class C and D,
4. The soil amplification factors depend on ground motion intensity. ECP (Eurocode 8) does not account for variation of soil amplification factors with ground motion intensity. ASCE7-16 code account for this variation.
6.2.4 Seismic capacity performance of multi-story buildings considering SSI with different soil types (B, C & D) in modelling
Three case studies (5, 10 & 15 stories) were analyzed to investigate Seismic capacity performance of Multi-story buildings (limited ductility) considering different soil types B, C & D in modelling. The response modification factor (R) has been determined considering the effect of number of stories of the building. The following results can be summarized:
1. Including soil in analytical models has a significant effect on the response modification factor (R) as its value decreases in soil-structure interaction models in all soil types (very dense soil B, medium soil C
& soft soil D), compared to fixed base type. Their lowest value was in soil type D and in highest building (2 basement + 15 super stories).
2. Maximum capacity ultimate base shear value decreases when considering SSI with soil types (very dense soil B, medium soil C
& soft soil D). It can be reduced by more than 10%. Moreover, the local damage of structural elements might collapse due to considering the soil.
3. Both ductility Rμ & over strength Rs values decrease when considering SSI with soil types (very dense soil B, medium soil C
& soft soil D). Their lowest values were in soil type (D) and in highest building (2 basement + 15 super stories).
4. Fundamental time period value increases when considering SSI with soil types (very dense soil B, medium soil C
& soft soil D). The highest value for fundamental time period was in soil type (D), soft soil making it a critical condition.
5. It could be concluded that the probability of reaching higher seismic damage increases when considering the SSI. Moreover, this increases with the height of the RC building.
6.2.5 Irregularity
Analysis models using 7 typical stories (Regular structure) versus 7 typical stories (Irregular structure) were used to study the effect for irregularity, the following was noticed;
- Converting the RC structure from regular to irregular leads to a smaller value for the base shear with a percentage of 13.8% and lower values for the R factor with a percentage of 18.8%.
- A reduction in R factor have to be considered in ECP when designing of an irregular structure. This reduction is 20% for irregular structures with reference to Eurocode8 (2012).
The following main points can be concluded:
1. The given value of R-factor at ECP-201 (2012) equals 5.0 for limited ductility class of reinforced concrete dual system from moment resisting frames and shear walls structures is unconservative value; as the accurate value of R-factor is less than the given value.
2. It’s recommended that the value of response reduction factor R for limited ductility class of reinforced concrete dual system from moment resisting frames and shear walls structures in ECP-201 (2012) to be changed to the used value in Eurocode-8 (2004).
3. It’s recommended that a reduction in R factor shall be considered in ECP when designing of an irregular structure, this reduction shall be around 20% as per study results & with reference to Euro code.
4. The soil amplification factors depend on ground motion intensity. ECP (Eurocode 8) does not account for variation of soil amplification factors with ground motion intensity. ASCE7-16 code account for this variation. Thus, it is recommended for ECP (Eurocode) to investigate the possibility of accounting for variation of soil amplification factors with ground motion intensity as considered in ASCE7-16 code. Analysis carried out in this thesis showed that there is a significant difference for soil amplification factor especially at small intensity ground motions for ECP (which is similar to Eurocode 8) site class B, C and D.
6.3 RECOMMENDATIONS
from the numerical analysis investigations presented in the present thesis, some recommendations for future research extension are suggested in order to investigate the following points:
1. Experimental studies in the field of inelastic behaviour of reinforced concrete frame system, and dual system structures having different levels of ductility.
2. Numerical studies for determining response reduction factor R for high ductility class of reinforced concrete frame system, and dual system structures.
3. Study the effect of the vertical and horizontal irregularity on the seismic response modification factor (R-factor) of reinforced concrete frame system, and dual system structures designed according to the Egyptian codes.
4. Study the effect of the reinforcement for different RC members (columns, beams, slabs & Raft) on the seismic response modification factor (R-factor) of reinforced concrete frame system, and dual system structures