AWARD WINNING SEISMIC ENGINEERS

Requirements For Soft-Story Retrofitting

Supervisor showing something to a colleague at construction site

At Army Of Builders, we specialize in soft-story buildings in Los Angeles, and in our experience we have seen that not every design is created suitable to meet the complete requirements for LA soft-story retrofit. Property owners often send us their plans looking for a quote on how much will the construction cost? In most cases, unfortunately, the services have to disappoint them by telling them their plans will not work.


Clients' Retrofit Plans

Most of the time, the client’s retrofit plans do not include enough reinforcements to protect the building during the event of major seismic activity. Very often, people simply focus on adding steel elements believing this will make their building sturdier. We have discovered that while the idea seems sound, in practice more enforced steel can easily collapse weakened wood-framed buildings.

With the Army of Builders, you will be to get drawn up a retrofit plan that covers all of the elements you need to prevent your building from collapsing in the next earthquake. One of the most essential elements that most people are missing, is the existing wood frame. Reinforcing and replacing worn-out or weakened word frames need to b part of any retrofit construction.

Steel Material In The Retrofit Process

Many of the engineering plans we see only focus on the strength and size of the steel being used in the retrofit (OMF/SMF moment frame, or OCCS/SCCS cantilever column). However, the steel material in the retrofit process is the most important part. Installing steel elements is much easier than designing these elements to work properly. While it may make you feel safer knowing steel columns have been installed if the retrofit designs do not include other elements they are flawed.

Without reinforcing the existing wood frame the steel columns could cause more damage during an earthquake rather than reducing it. Steel is a stiff element and during the trembling of an earthquake, it may fall or collapse, demolishing the wood in its way. A major quake will push the wood components into the stiff steel and cause them to buckle or break.

Retrofitting Wood-Frame Structures

Army of Builders’ engineers have years of experience retrofitting wood-frame structures and they know how to draw up plans that allow seismic loads to transfer correctly. Almost all of the plans created by other companies or even building owners do not take the wood frame itself into consideration.
Stack of wood-frame of a house under construction

In the event of a major earthquake, your building could come tumbling down. Meaning all the money you invested in your retrofit would be for nothing. One of the biggest reasons for these design flaws is the wording of the Los Angeles soft-story retrofit ordinances which do not mention the need for reinforcing wood frames. For this reason, you will want to make sure you hire a retrofit company that is experienced with seismic retrofits for wood-framed structures.

Simpson Strong-Tie Connection

A complete retrofit design needs to include the reinforcement of the wood frame that is already in place. One way to accomplish this is to add new connections, such as Simpson Strong-Tie LTP4/LTP5 and A34/A35 plates. This step helps to create a sturdy structure that transfers earthquake loads evenly and ensures the building will remain standing in the event of a major seismic event.
The first step is to remove the stucco covering the frame. This allows the contractor to assess the weak areas. We like to use a combination of wood boards to create a block and installing more steel connectors like Simpson Strong-Tie LTP 4 connectors over the new blocking. This provides a design that allows the subfloor to resist torsion and ties it to the existing dragline beam.

Transfer Of The Earthquake’s Forces

By installing wood blocking above a steel moment frame, we create a solid connection. This provides a transfer of the earthquake’s forces between the new frame and the existing building. After that, we run the wood blocking through the length of the structures. Now we have made more connections between the new and old structures which let them work together. By creating a larger blocking frame it is more likely that the shaking of an earthquake will transfer smoothly back to the steel moment frame. Our team of specialists puts a lot of thought and detail into crafting our retrofit designs. They work to ensure the soft-story retrofit will not just be strong enough but also smart enough to protect your building.

Earthquake Retrofitting Techniques and Strategies

Earthquake Retrofitting Techniques and Strategies are required for constructions that are vulnerable to damage and failures by seismic forces. In the past 30 years, moderate to severe earthquakes occur around the world every year. There are several exact categories of retrofitting techniques:

  • External post-tensioning

  • Base isolators

  • Supplementary dampers

  • Tuned mass dampers

  • Slosh tank

For more information check our article about retrofitting techniques and strategies.

Seismic retrofit strategies are made within the past several decades following the availability of advanced materials and the introduction of new seismic provisions.

  • Increasing global capacity. This is done by the new structural walls or the addition of cross braces

  • Selective weakening retrofit. This is a strategy that does not happen in a way someone would expect it to and it changes the non-flexible mechanism of the structure while recognizing the inherent capacity of the structure

  • Accepting sliding connections, for example, passageway bridges to accommodate additional motion between seismically independent structures and more.