technicalcase-study
Seismic Retrofitting: Lessons from the Transit Hub Project
Saida Bilqiis Bajeh, GMNSE
1/15/2024
8 min read
# Seismic Retrofitting: Lessons from the Transit Hub Project
## Introduction
When the Metro Transit Authority approached us about renovating the Downtown Transit Hub, one of the most challenging requirements was bringing the 40-year-old structure up to current seismic codes—all while keeping the facility operational 24/7.
## The Challenge
The original 1982 design predated significant updates to seismic building codes. Our structural assessment revealed several critical deficiencies:
- **Column Design**: Original columns lacked adequate confinement reinforcement
- **Foundation Connections**: Insufficient anchorage for lateral forces
- **Diaphragm Action**: Weak floor-to-wall connections
- **Soft Story Risk**: Ground floor configuration created lateral instability
## Our Approach
### 1. Base Isolation System
We implemented a base isolation system using friction pendulum bearings. This approach offered several advantages:
- Reduced seismic forces transmitted to superstructure by 60-70%
- Allowed preservation of more original structural elements
- Minimized disruption to daily operations
- Cost-effective compared to complete column replacement
### 2. Phased Implementation
The key to maintaining operations was our 6-phase approach:
**Phase 1-2**: Install temporary shoring and support systems
**Phase 3-4**: Retrofit foundation and install isolation bearings
**Phase 5-6**: Structural reinforcement and connection upgrades
### 3. Column Jacketing
For columns that couldn't be replaced, we used fiber-reinforced polymer (FRP) jacketing:
```
Material: Carbon fiber sheets with epoxy matrix
Thickness: 3-5 layers depending on column condition
Installation time: 48 hours per column (including cure time)
Strength increase: 40-60% in confinement capacity
```
## Results and Takeaways
The completed retrofit exceeded performance requirements:
- **Seismic Performance**: Structure can withstand 1.5x code-required forces
- **Schedule**: Completed in 20 months vs. 24-month estimate
- **Operations**: Zero service interruptions during construction
- **Cost**: 15% under budget through innovative solutions
## Key Lessons
1. **Early Engagement**: Involving all stakeholders from day one prevented costly changes
2. **Temporary Works**: Investing in robust temporary support systems paid dividends
3. **Technology**: FRP composites offered speed and performance advantages
4. **Monitoring**: Real-time structural monitoring provided confidence during retrofit
## Conclusion
Seismic retrofitting of operational facilities requires careful planning, innovative solutions, and flawless execution. The Transit Hub project demonstrated that even the most challenging constraints can be overcome with the right approach.
*Have questions about seismic retrofitting for your facility? [Contact us](/contact) to discuss your project.*
## Introduction
When the Metro Transit Authority approached us about renovating the Downtown Transit Hub, one of the most challenging requirements was bringing the 40-year-old structure up to current seismic codes—all while keeping the facility operational 24/7.
## The Challenge
The original 1982 design predated significant updates to seismic building codes. Our structural assessment revealed several critical deficiencies:
- **Column Design**: Original columns lacked adequate confinement reinforcement
- **Foundation Connections**: Insufficient anchorage for lateral forces
- **Diaphragm Action**: Weak floor-to-wall connections
- **Soft Story Risk**: Ground floor configuration created lateral instability
## Our Approach
### 1. Base Isolation System
We implemented a base isolation system using friction pendulum bearings. This approach offered several advantages:
- Reduced seismic forces transmitted to superstructure by 60-70%
- Allowed preservation of more original structural elements
- Minimized disruption to daily operations
- Cost-effective compared to complete column replacement
### 2. Phased Implementation
The key to maintaining operations was our 6-phase approach:
**Phase 1-2**: Install temporary shoring and support systems
**Phase 3-4**: Retrofit foundation and install isolation bearings
**Phase 5-6**: Structural reinforcement and connection upgrades
### 3. Column Jacketing
For columns that couldn't be replaced, we used fiber-reinforced polymer (FRP) jacketing:
```
Material: Carbon fiber sheets with epoxy matrix
Thickness: 3-5 layers depending on column condition
Installation time: 48 hours per column (including cure time)
Strength increase: 40-60% in confinement capacity
```
## Results and Takeaways
The completed retrofit exceeded performance requirements:
- **Seismic Performance**: Structure can withstand 1.5x code-required forces
- **Schedule**: Completed in 20 months vs. 24-month estimate
- **Operations**: Zero service interruptions during construction
- **Cost**: 15% under budget through innovative solutions
## Key Lessons
1. **Early Engagement**: Involving all stakeholders from day one prevented costly changes
2. **Temporary Works**: Investing in robust temporary support systems paid dividends
3. **Technology**: FRP composites offered speed and performance advantages
4. **Monitoring**: Real-time structural monitoring provided confidence during retrofit
## Conclusion
Seismic retrofitting of operational facilities requires careful planning, innovative solutions, and flawless execution. The Transit Hub project demonstrated that even the most challenging constraints can be overcome with the right approach.
*Have questions about seismic retrofitting for your facility? [Contact us](/contact) to discuss your project.*