Why older walls come apart
A retrofit buys one thing: a path for the load to travel from the roof to the ground. In a tilt-up or masonry building the heavy wall panels and the light wood roof are two different animals bolted together, and the state's guide for commercial property owners describes what happens when those connections are weak: the walls pull away from the floors and roof during shaking, and the roof loses what was holding it up.
The year the building went up decides most of the scope. Poor anchorage is likeliest where precast tilt-up or masonry walls went up before the mid-1970s, and it turns up in some buildings from 1975 to 1995 as well. The fix is new anchorage and continuous ties across the roof, worked either from inside above the ceiling or from the roof side.
Brick, older concrete and older steel each fail their own way. In unreinforced masonry the parapets, cornices and wall tops go outward and the walls separate from the diaphragms, so the retrofit ties the walls to the roof and floors and adds steel frames or reinforced concrete. Pre-1980 concrete walls and columns often lack enough reinforcement, and are answered with new walls, bracing or column wraps. Pre-1995 steel moment frames and pre-1982 braced frames often need work of their own. Cladding and signage anchorage comes into the same survey.
A duty attaches to an older building whether or not it is retrofitted. On the sale of a precast concrete or reinforced masonry building with wood frame floors or roofs built before January 1, 1975, Government Code 8893.2 has the seller deliver the state's earthquake safety guide as soon as practicable before the sale, and the same applies to an unreinforced masonry building of that age.
What seismic retrofit includes
The building's age, wall type and roof framing are established first, because they decide whether anchorage, wall strengthening, bracing or wraps is the scope. An engineer's evaluation follows, and it produces the drawings the work is built to. Original plans shorten this step considerably.
The drawings are prepared under the California Building Standards Code, and the route chosen is stated on them, so the building department reads the same document the crew builds from.
The application goes to the building department for the jurisdiction the property sits in. A retrofit needs a permit, and a historic building may bring the historical code with it.
Anchors are drilled and set, and continuous ties are run across the roof. Drilling into concrete and masonry runs under the dust controls in Title 8 section 1532.3.
Where the drawings call for them: new shear walls, steel frames, parapet bracing, and confining wraps around columns built without enough steel.
The permit is finalled, and the plans, the permit and the project records go to the owner, who hands them to a future buyer along with the building.
A retrofit is bought for a continuous load path, not for a list of parts. Anchors, ties, frames and wraps are worth only what the weakest connection between them will carry, so the scope follows the path and not the elevation.
Where a retrofit is needed
Tilt-up warehouses and distribution
Concrete panels carried on a wood or light roof diaphragm, where the anchorage between the two is the whole question and the racking underneath is the exposure.
Cold storage and processing
Same wall and roof pairing, with insulated panels, refrigeration plant and process equipment hung off the structure, so the survey covers what the walls are carrying as well.
Downtown brick blocks
Unreinforced masonry with unbraced parapets and cornices over the footway, header courses in the brickwork, and floors that were never tied into the walls.
Older concrete offices
Pre-1980 frames and shear walls where the columns lack confining steel, usually answered with added walls or bracing and wraps at the columns that carry most.
Older steel-frame buildings
Moment frames from before 1995 and braced frames from before 1982, where the connections sit behind finishes and an assessment comes before any scope.
Cladding, parapets and signs
Panels, veneers, roof-top signs and canopies anchored to older walls, which are the elements that reach the footway first and are surveyed with the walls they hang on.
Questions about seismic retrofit
Not by state law in this part of California. The state's unreinforced masonry programme binds only jurisdictions inside the 1985 Seismic Zone 4, and where a city's own file records an ordinance, that city's page follows it. Substantial structural damage changes the position here: an evaluation follows.
Usually, with phasing. Anchorage work is often done from inside above the ceiling or from the roof side, which keeps it out of the tenant space. Frames and shear walls are put in one line at a time. The site visit is where the sequence around occupancy is settled.
Almost everything about the scope. It sets which wall and frame type the building is, which of the state's disclosure categories it falls in, and whether the anchorage between the walls and the roof was designed to a standard that still stands. Original plans answer it fastest.
It is, and it is controlled. Anchor and dowel holes in concrete and masonry are drilled with a shroud and dust collection or with water fed to the bit, and the holes are cleaned with a vacuum rather than blown out.
The plans, the permit and the project records. They are what a future buyer is given with the building, and what the next engineer reads before proposing anything, so they are kept together rather than filed apart.
Seismic retrofit by city
A retrofit is requested through the structural repair page for your city, which names the department that permits the work there.
Related structural repair services
