Reinforced and unreinforced masonry
by Admin
Posted on 09-09-2024 10:35 AM
Experience from christchurch and overseas has shown that the failure of earthquake-prone buildings, or parts, can endanger lives. Thirty-nine people lost their lives when unreinforced masonry buildings failed during the christchurch earthquake on 22 february 2011. Earthquake risk reduction is a priority in new zealand.
New zealand has had a progressive approach to improving standards for new buildings and earthquake-resistant design since design standards for buildings were first introduced into new zealand in 1935, following the napier earthquake. Advancements in the knowledge of seismicity, material properties and the response of buildings in earthquake shaking has resulted in progressive refinements to requirements for the design and detail of buildings.
As a capstone to several mid-america earthquake center (mae center) projects, a full-scale two story unreinforced masonry (urm) building was tested following the application of several retrofit techniques, which included the use of fiber reinforced polymer (frp) overlays, near surface mounted (nsm) rods, vertical unbonded post-tensioning, and joist anchors. The test structure was composed of four urm walls, flexible timber diaphragms and interior stud walls, and was designed and built following construction practices consistent with those used in mid-america prior to 1950. Initial testing subjected both the roof diaphragm and in-plane walls to slowly applied lateral load reversals in an unreinforced sate. https://en.wikipedia.org/wiki/Glued_laminated_timber
A whole building or a part of a building can be earthquake prone. This means that engineers assessing potentially earthquake-prone buildings need to consider vulnerable parts of buildings, such as unreinforced masonry parapets, as well as the overall performance of the whole building. A part is an individual building element – such as a unreinforced masonry parapet – which would pose a life safety hazard if it fell or caused another building element to fall during a moderate earthquake. The methodology to identify earthquake-prone buildings sets out how engineers are required to consider and report on parts of buildings when undertaking an engineering assessment.
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The city has engaged in a three community outreach meetings to describe the proposed draft ordinance and collect input from the community were virtually held on the following dates:
november 03, 2020.
Our planet is covered by tectonic plates that are slowly moving around, pushing into or sliding past one another along boundaries called faults. Friction sometimes causes two of these plates to get stuck to each other at spots along a fault. Tension builds up over years, decades or even centuries until suddenly the fault snaps. The two sides lurch past each other, unleashing an earthquake. From the place where the fault ruptures, seismic waves ripple outward in all directions. When they reach earth’s surface, they can set buildings or any other structures shaking—violently and destructively if the quake is strong and close enough, as were the two massive temblors that struck turkey and syria on february 6, which was followed by a large aftershock on the same day.
The city of beverly hills is taking a proactive approach to earthquake safety with the goal to help protect people and minimize damage of vulnerable buildings in the event of a major earthquake. As such, the city has developed a mandatory seismic retrofit ordinance intended at strengthening existing wood-frame multi-family soft-story buildings. The new ordinance (no. 18-o-2767) was adopted at the december 11, 2018 formal city council meeting. The ordinance became effective on january 11, 2019. The new mandatory ordinance addresses soft-story buildings which are most vulnerable and have been identified with the following criteria: a permit for construction of a new building was applied for before january 1, 1978, or if no permit can be located, the structure is determined by the city building official to have been built under building code standards enacted prior to january 1, 1978, and.
What Are Building Codes?
Building codes are sets of regulations governing the design, construction, alteration and maintenance of structures. They specify the minimum requirements to adequately safeguard the health, safety and welfare of building occupants. Rather than create and maintain their own codes, most states and local jurisdictions adopt the model building codes maintained by the international code council (icc). The icc’s family of international codes includes: international building code (ibc): applies to almost all types of new buildings international residential code (irc): applies to new one- and two-family dwellings and townhouses of not more than three stories in height international existing building code (iebc): applies to the alteration, repair, addition or change in occupancy of existing structures.
A soft story building is one that has either parking or commercial space on the first floor, and residential units on higher stories. These buildings were constructed prior to current codes and are can be at risk of collapsing in large earthquakes.
In some earthquake-prone regions, local building codes or ordinances may require certain buildings, particularly older ones, to undergo seismic retrofitting to comply with safety standards. Building owners should consult with local authorities to determine if retrofitting is mandatory for their properties.
When it comes to resilience during a major earthquake, some homes perform better than others. This largely has to do with when a structure was built — more specifically due to the building standards at the time of its construction. Homes built before 1985, for example, and particularly those built on raised foundations, can be especially susceptible to earthquake damage. Fortunately, advances in structural engineering, lessons learned from past earthquakes and scientific research have paved the way for construction techniques that better equip homes to withstand a seismic event. And local and regional building codes now require all new houses in seismically vulnerable regions to meet higher construction and safety standards.
Earthquakes occur when tectonic plates in the earth’s lithosphere (the mantle and crust) grind together and then suddenly shift. The shift produces a massive energy release that travels from the epicenter through the ground in concentric waves. These waves then move through structures in both vertical and horizontal waves, stressing foundations, walls, and connections between materials. Most structures are designed to handle vertical forces, such as gravity and their own weight. They fail in an earthquake primarily because of the horizontal forces, which normal building codes don’t account for. You can also view structural failure in terms of harmonics.
Recent studies highlight the majority of existing structures located in the seismic-prone regions all over the world often found to be designed with poor or without the consideration of the seismic designs and/or are variously incompetent in the sight of the principles of seismic designs used currently. Earthquakes, even with a moment magnitude of 6. 0 are capable of causing extensive loss of structural compatibility and hence structures need to be evaluated in the sight of the current codes available and provisions of retrofitting should be incorporated, if necessary. In this study, a school building located in imphal, manipur was considered and conducted a vulnerability assessment through incorporation of preliminary and detailed assessment analysed by etabs 2018 software with pushover analysis.