Earthquake An earthquake (also known as a tremor or temblor) is the result of a sudden release of energy in the Earths crust that creates seismic waves. Earthquakes are recorded with a seismometer, also known as a seismograph.
WHAT CAUSES EARTHQUAKES? Earthquakes are caused mostly by rupture of geological faults, but also by volcanic activity, landslides, mine blasts, and nuclear experiments. But most naturally-occurring earthquakes are caused by the movement of the earths tectonic plates.
ONE OF THE MOST DIFFICULT SETS OF FORCES FOR ENGINEERS TO ASSESS IS THAT CAUSED BY EARTHQUAKES. The base shear and distribution of forces are based on the properties of the building itself, as well as the ground motions of an earthquake, which are impossible to predict. In addition, the actual stiffness of a building is only an estimate and can change during the earthquake as members yield.
A Possible Solution to the EARTHQUAKES To survive a large earthquake, a building’s structure must dissipate the energy imparted by the ground accelerations. Introducing a fuse into the structural frame can provide this dissipation, as well as create a predictable structural response to an unpredictable set of forces.
FUSEThe word fuse has several meanings: Fuse (electrical), a device used in electrical systems to protect against excessive current. Fuse (hydraulic), a device used in hydraulic systems to protect against sudden loss of fluid pressure Fuse (explosives), a trigger for an explosive device or fireworks, also spelled fuze to distinguish between a simple burning fuse and one which contains mechanical and/or electronic components
Earthquake FuseIt is an Analogy of an Electrical Fusethat allows the dissipation of extraenergy from the system bydisconnecting itself from the mainStructure thereby making theremaining structure less affected.
The Fuse Concept Non- Structural components (i.e. other than main structure) having mass are added to the structure so that at the time of Ground Motion they allow the dissipation of extra energy from the system. The Fuse gets disconnected from the main Structure thereby making the remaining structure less affected. By forcing the ductility demand to the fuses, the behavior of the system becomes more predictable.
These members are generally required to have low width-to-thickness ratios to avoid local buckling, and eventually fractures, well into the elastic range. The remaining frame members are designed to remain essentially elastic while the fuse yields dissipate the energy. These members are often sized based on the expectation that the fuse is the overloaded element in the system.
The Structural Fuse:An Inelastic Approach to Earthquake- Resistant Design of Buildings
The Structural Fuse An alternative to the empirical approach to earthquake-resistant design of buildings is the Structural Fuse. Instead of strengthening every member to resist deformation under earthquake loads, deliberately makes some members, mostly beams, weaker, so that they will yield in a controlled fashion during an earthquake. Yielding beams dissipate energy, reducing stress on the more crucial columns and walls.
Structural Fuse Structural fuses help increase the predictability of a building’s behavior and dissipate seismic energy in the event of an earthquake. The FUSE must be highly DUCTILE, it will have to accommodate most of the Imposed Deformations.
Why Structural Fuse ? In seismic design, the loads resulting from an earthquake are reduced by a response modification factor, which allows the structure to undergo inelastic deformations. This methodology relies on the ability of the structural elements to accommodate inelastic deformations. Furthermore, inelastic behavior translates into some level of damage on these elements.
This damage leads to permanent system deformations following an earthquake, leading to high cost for repair works, in the cases when repairs are possible. To achieve stringent seismic performance objective for buildings, an alternative design Approach is desirable. In that perspective, it would be attractive to concentrate damage on disposable and easy to repair structural elements (i.e., “structural fuse”), while the main structure would be designed to remain elastic or with minor inelastic deformations.
Fuse Device Behavior
Ductile elements were used to reduce inelasticdeformations of the main Structure.
Our Focus: Plastic Hinge Pinned connection between column and foundation. Rotation prevented by small vertical members. These small bars act as fuses, allowing rotation before yielding of column - called Fuse Bars.
Functions of Plastic Hinge Type of energy dampening device. Yielding and subsequent deflection of fuse bars absorb energy. Reduces fatigue in column during repeated ground motion. Post-earthquake, fuse bars can be replaced relatively easily. Column-hinge system is then restored to original condition.
Results in: Stiffness of column-hingesystem lower than expected. Rotational stiffness muchless than expected.
Benefits of Fuse Concept Seismically induced damage is concentrated on the fuses. Following a damaging earthquake only the fuses would need to be replaced. Once the structural fuses are removed, the elastic structure returns to its original position.
Conclusions Energy dissipation protects column from excess strain and fatigue. Fuse-bars designed to be replaced easily after they wear out. Additional energy can be absorbed by small component yielding or slipping. (Not desired, may wear out component over time )
PrincipleThe most important is to "remain calm, and secure yourpersonal safety based on your surroundings.
What To Do In the Event of anEarthquake Prepare a Home Earthquake Plan. Prepare a Disaster Supplies Kit for home and car. Identify what to do after the shaking stops. Examine walls, floors, doors, staircases, and windows for damage. Look for fire hazards. Check for gas leaks or electrical system damage. Help injured or trapped persons. Use the telephone only for emergency calls.
REFERENCES Analysis of Rotational Column with Plastic Hinge Michael Long and Corey Bergad retrieved November 5, 2006. "Plastic Hinge Integration Methods for Force-Based Beam- Column Elements." Scott, M.H. and G.L. Fenves. Journal of Structural Engineering, 132(2):244-252, February 2006. Seismic Fuses (BY JASON ERICKSEN, S.E). Understanding the basics of earthquake design (BY DAVE TIPLER, P.ENG). Investigation of the Structural Fuse Concept Ramiro Vargas and Michel Bruneau