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Strengthening Existing Buildings

In many parts of the country, including the mid-South, When renovating an older building, it is rare to strengthen it to the performance standards of new construction. The required strengthening tends to be a gray area, where an engineer has some latitude. We approach this case-by-case based on factors such as the customer’s needs, the age and condition of the building, historical precedent for similar projects, and any directives by the jurisdiction.

Most older buildings have severe seismic liabilities that were not accounted for when the building was built. Add to this the reality that the brick, mortar, and wood framing have all deteriorated and may continue to degrade due primarily to moisture infiltration and trapping. Also, consider that the proposed renovation will further weaken the building by increasing or adding wall and floor openings as well as material weights. Or even just by removing the lath and plaster sheathed studwall partitions and opening up a floor plan, we are also weakening the structure. These changes may trigger strengthening requirements in the IEBC. Yet in our region, the design engineer and the governing jurisdiction often ignore these triggers.

Is this what the owners and architects want? They are investing in a building, expecting that their investment is sound and that the building is safe.

At Ozer, we have a high standard of care. We will only work on a building if we can include repairs or strengthening so that when the project is complete, the structure overall is a little stronger and more resilient than it was when we found it.

Our rule is that when we are done, we leave a building stronger and safer than when we found it, even if we can't make it as strong as a new building.

For example, removing a bearing wall to open up space may weaken the building because that brick-bearing wall serves as a shear wall. So we will add connecting elements to deliver the lateral forces to other parts of the remaining shear wall. Or we may need to strengthen other walls or as a last resort, install new shear walls. That's why we often give the owner a couple of options. The minimum option is it's a little stronger and more resilient than how we found it. The better option is we've fully implemented the IEBC requirements. In either case, the completed renovation can better handle an overload such as a big storm or small earthquake.

And it also means we've arrested the decay; some older materials break down much quicker than modern materials. In particular, the old brick and lime mortar, if it's a brick structure. In other cases, deterioration of the wood or steel has begun, and we want to identify and address the source of the moisture intrusion or treat the wood, masonry or steel to protect it down the road. And this is sometimes a complex procedure.

Sometimes we are on the defensive; the owner wants to do the bare minimum as they see it: remove the wall and provide gravity supports at the affected area. In such cases, we walk away from the project. For better or worse, other engineers will do the job just as he wishes.

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