It may seem that earthquakes are happening now more frequently. However, they are a pretty common occurrence. What is not that common - is the strength of the quakes that have rocked the world in the last decade. After facing some significant earthquake disasters, and passing the Retrofit Program Law now we can see more retrofitted structures throughout the city. For example in 2010 and 2011, Chile was hit with numerous quakes, ranging from mild to 8.8 quakes that hit the coast near Concepcion. Japan also experienced a major quake, measuring 9.0 that caused the popular tsunami and over 29,000 human lives were taken by that. The United States has had its part of seismic activity as well. In the summer of 2011, a 5.8 earthquake hin near Mineral, Virginia. So the California residents felt the effects of the back-to-back shakings a couple of years back. These recent events have LA soft-story retrofit companies aiming to create buildings that can sustain the next major earthquake.
Creating Earthquake-Proof Buildings
No matter the circumstances, human beings are hard-wired to survive. Our will to survive has helped us to achieve amazing advances in the industry of technology, medicine and, of course, engineering creating earthquake-proof buildings. Within the centuries, engineers have learned how to adapt building designs to create structures that will last for centuries, so creating earthquake-proof earthquakes is not a new idea.
Many old structures and buildings, constructed in seismic areas, are standing today. Let’s discuss the Hagia Sophia church case. It was built in 573 A.D, in Istambul and about 20 years after its completion the area was hit with an earthquake. It damaged the huge dome on the church collapsed it. Engineers assessed the damage and adapted a new design to make the next dome ore quake-proof. The new dome was smaller than the original and they reinforced the church from the outside.
Many engineers and scientists agreed that with nowadays technology it is possible to build earthquake-proof structures. Although the prices are going to be amazingly high, it well worth, for most experts have chosen to focus on the next best thing earthquake-resistant buildings. The retrofitted structures are designed to prevent loss of life and complete collapse during an earthquake.
First of all, for constructing a new building you need to determine the potential for seismic activity zones. There are National Seismic Hazard Maps designed. This collection of maps can provide soft-story retrofitting companies. They can determine the possibility of seismic activity in an area within the next 50 years.
Geologists use historical information to make an educated guess about the motion of the Earth’s crust and the possible magnitude of an earthquake. This formula is taking into account all the data not just from the main location, but from areas around it as well. Then they create a colored map that demonstrates the zones around the country that are most likely to be earthquake-prone. It is not surprising for the LA residents that the coast of California is a high hazard zone.
Cities now can create building codes that establish guidelines for earthquake-resistant structures with the help of those geological maps. Contractors and engineers must design and build all the structures, such as apartment complexes, bridges, and office buildings to meet these strict seismic codes.
Design Components Of Earthquake-Resistant Buildings
The first component of an earthquake-proof design is the shape of the building. For example, in high hazard areas, asymmetrical designs, such as T and L-shaped, structures should be avoided. Besides the pleasing visual, they are more vulnerable to twisting or collapsing because of the forces of an earthquake. Symmetrical designs, however, are the best ones as long as they can help to distribute the forces evenly throughout the building.
Although, even symmetrical buildings can be vulnerable to the lateral forces hit be a major earthquake. The forces of vertical and horizontal structural systems need to be considered during designing the building to resist lateral forces.
The vertical structural system is designed to transfer the forces of an earthquake to the ground. Several components used by many engineers include columns, bracing and beams. Some buildings include walls having braced frames, and these trusses help them to resist the side-to-side motion created during a quake. Many buildings, along with those braced frames have a shear wall that is used to make the buildings sturdier.
Shear walls are usually found near stairwells and elevators. Shear walls do limit the flexibility of the building design. In these structures, the beams and columns are allowed to bend, but the connectors and joints between them are rigid. Aa a result the whole frame moves in response to a lateral force and offers an edifice that is less obstructed internally than shear-wall buildings. Through this, the designers can be flexible during placing architectural elements, such as exterior walls, ceilings, petitions and building contents, such as furniture and loose equipment.
The drawback with shear walls is they hinder a building’s flexibility. Engineers often add moment-resisting frames allowing the columns and beams to bend but keep the connectors rigid. This allows the whole frame to move with the force of an earthquake while still providing support to the buildings.
The seismic retrofit is used to be primarily applied to achieve public safety, with engineering solutions limited by political and economic considerations. However, with the development of Performance-based earthquake engineering, several levels of performance objectives are gradually recognized:
Public safety only - the goal is to protect human life, ensuring that the structure will not collapse upon its occupants or passersby and that the structure can be safely exited. Under severe seismic conditions, the structure may be a total economic write-off, requiring tear-down and replacement.
Structure survivability - the goal is that the structure while remaining safe for the exit, may require extensive repair (but not replacement) before it is generally useful or considered safe for occupation. This is typically the lowest level of retrofit applied to bridges.
Structure functionality - the primary structure undamaged and the structure is undiminished in utility for its primary application. A high level of retrofit ensures that any required repairs are only "cosmetic" – for example, minor cracks in plaster, drywall, and stucco. This is the minimum acceptable level of retrofit for hospitals.
Structure unaffected - this level of the retrofit is preferred for historic structures of high cultural significance.
City Ordinances Requiring Earthquake Retrofit
Retrofit ordinances can be complicated and city-specific, Partner has expertise navigating them and guiding clients through the myriad finance options.
Los Angeles passed a mandatory retrofit ordinance. The LA ordinance is requiring the structural strengthening of two of the city’s most vulnerable building types: wood-framed soft-story buildings that are built before 1978 and non-ductile concrete buildings built before 1977 Financing and funding options are explored.
Berkeley, Fremont, Oakland, San Jose, Campbell, San Leandro, Burbank, Santa Monica, Pasadena, Portland, Seattle, and other communities have implemented or are drafting mandatory and voluntary seismic retrofit ordinances and programs. The list of cities considering or enacting retrofit ordinances is likely to keep on growing and Partner is committed to keeping up to date with their requirements.
And the San Francisco Mandatory Soft-Story Retrofit Ordinance was created by the San Francisco Community Action Plan for Seismic Safety, targets wood-frame buildings built before 1978 which have three or more stories and five and more residential units with remarkable ground floor openings.
Army Of Builders is an expert in designing retrofit options; Our service combines the understanding of our client’s business with our structural engineering experience to arrive at a retrofit solution. Some of the common methods employed to retrofit soft-stories include the installation of:
Plywood Shear Walls
Concrete Shear Walls
Braced or moment-resisting Steel Frames
Cantilevered Steel Columns
Foundations and Grade Beams
Foundation, Roof and Wall Anchors
Strengthening Unreinforced Walls
Jacketing of Columns