Final Project Topics Seismic Control of Structures for Dynamic Actions
A Brief Review of Fundamentals of Earthquake Resistant Design
Earthquake Engineering can be defined as the branch of engineering devoted to mitigating earthquake hazards. In this broad sense, earthquake engineering covers the investigation and solution of the problems created by damaging earthquakes, and consequently the work involved in the practical application of these solutions, i.e. in planning, designing, constructing and managing earthquake-resistant structures and facilities. Title: Roof-top water tank induced damage Date: 2001 Earthquake: Bhuj, India earthquake, Jan. 26, 2001 Magnitude: 7.7
General Goals in Seismic-Resistant Design and Construction The philosophy of earthquake design for structures other than essential facilities has been well established and proposed as follows: a.To prevent non-structural damage in frequent minor ground shaking b.To prevent structural damage and minimize non-structural damage in occasional moderate ground shaking c.To avoid collapse or serious damage in rare major ground shaking Title: Damage from out-of-plane deformation Location: Turkey/ASIA/Western Asia Earthquake: Izmit, Turkey earthquake, Aug. 17, 1999 Magnitude: 7.4
Building structures may be of many types and configurations and there is, of course, no universal ideal configuration for any particular type of building. However, there are certain basic or guiding principles of seismic-resistant design that can be used as guidelines in selecting an adequate building configuration structural layout, structural system, structural material and the non-structural components. These basic guidelines are as follows:
1. Building (superstructure and non-structural components) should be light and avoid unnecessary masses.
Superstructure should have the largest possible number of defense lines, that is, it should be composed of different tough structural subsystems which interact or are interconnected by very tough structural elements (structural fuses) whose inelastic behavior would permit the whole structure to find its way out from a critical stage of dynamic response. Plan view of the Banco de America, Managua, Nicaragua. This building generally performed very well during the 1972 Managua Earthquake. Its excellent performance can be attributed to the symmetry and uniformity of distribution of the masses and structural stiffnesses throughout the building.
2. Building and its superstructure should be simple, symmetric, and regular in plan and elevation to prevent significant torsional forces, avoiding large height-width ratio and large plan area.
Hotel Terminal, Guatemala City. Overall view of this 6-story hotel, illustrating the torsional failure of the second story during the 1976 Guatemala Earthquake.
Refer to type of irregularities in structures
3. Building and its superstructure should have a uniform and continuous distribution of mass, stiffness, strength and ductility, avoiding formation of soft stories.
Commercial Building Casa Micasa S.A., Managua, Nicaragua. This 2-story reinforced concrete frame building suffered significant lateral displacement at the second floor level during the 1972 Managua Earthquake.
Detailed view of the behavior of one of the first and second story columns in the building of Slide J72 during the 1971 San Fernando Earthquake. Note the large permanent distortion of the first story column (because it was part of the soft story at this level). While the well-confined concrete of the spirally reinforced core of this column was capable of holding the building up, the unconfined concrete cover had spalled off. Note also the shear failure of the second story column, induced by the shortening of this column by the wall panels that were placed at the top and bottom of this story.
Olive View Hospital, Psychiatric Unit, San Fernando, California. 1971 San Fernando Earthquake. This unit was a 2-story reinforced concrete building. The structural system was a moment resisting frame. However, in the second story there were masonry walls that added significantly to the stiffness of this story.
Two-story reinforced concrete building, Managua, Nicaragua, damaged in the 1972 Managua Earthquake. The slide shows a reinforced concrete column which was part of the structural system and which failed due to its shortening because of the effect of the masonry wall. The masonry walls were considered as non-structural elements.
4. The non-structural components should either be well separated so that they will not interact with the rest of the structure, or they should be integrated with the structure. On the latter case, it is desirable that the structure should have sufficient lateral stiffness to avoid significant damage under minor and moderate earthquake shaking, and toughness with stable hysteric behavior (that is, stability of strength, stiffness and deformability) under the repeated reversal of deformations which could be induced by severe earthquake ground motion. The stiffer the structure, the less sensitive it will be to the effects of the interacting non-structural components, and the tougher it is, the less sensitive it will be to effect of sudden failure of the interacting non-structural elements.
Innovative Earthquake Resistant Design and Control Methods
Motivation for Controlling of Earthquake Forces • Control earthquake forces in order to • Obtain better building performances • Controlling can be through design details, passive control or active control
PED: Passive Energy Dissipation
An Example for a Passive Control Seismic Isolation Seismic Isolation Technologies The basics – How it works? Design related issues
Seismic Performance Goals Our goals are to Preserve Life Safety and Prevent Collapse
Van Earthquake 2011 - Turkey
Total collapse
If collapse can be prevented, which level of damage is acceptable? L’Aquila Earthquake 2009 - Italy
Local Failure
Permanent Failure
Seismic Performance Goals In Earthquake Engineering the challenge is to build structures for different performance levels (e.g.,): Life safety for strong eartquakes (rare events), Limited damage for design based eartquakes.
RESILIENT STRUCTURES
Ductility Design vs. Force Control Strategy Challenges in “ductile design” strategy: Strong column – weak beam mechanism may not form due to existence of wall, Shear failure of columns may occur due to wrong proportioning or short-column effect, Construction difficulty at beam-column joints due to complexity of steel reinforcement,
So, why not control the inertial forces attracted to the structure?
Seismic Isolation – Controlling Forces How It Works? The structure is decoupled from the ground by isolators with low horizontal stiffness, This results in fundamental frequency that is much lower than the fixed-base frequency, The first dynamic mode of the isolated structure involves deformation only in the isolation system,
Seismic Isolation – Controlling Forces How It Works? These higher modes do not participate in the motion, reducing drift (orthogonality), The isolation system does not absorb the earthquake energy, but rather deflects it through the dynamics of the system.
Building with a Seismic Isolation
Building with a Seismic Isolation
Schematic representation of a building with base isolation system
Seismic Isolation With a seismically isolated structure, the seismic forces are reduced, this leads to: Smaller structural members Smaller foundations Smaller accelerations
Seismic Isolation How It Works? – A Demonstration!
Seismic Isolation Requirements of a Base Isolated Device 1. Isolating the building from the ground,
2. Supporting the weight of the structure,
Seismic Isolation Requirements of a Base Isolated Device 3. Damping of response amplitude,
4. Restoring to the original position after an earthquake,
Seismic Isolation Isolated Building
Increasing the period will reduce the acceleration
Seismic Isolation
Isolated Building
Increase in period will increase the displacements, therefore high damping is needed!
Seismic Isolation Types of Isolators Laminated elastomeric bearings,
Video
Types of Isolators Pendulums (low friction sliders – stainless steel/PTFE)
A Test Video of a Friction Pendulum
Types of Isolators Elasto-plastic devices
Devices at Bolu Viaducts
Application of anti-seismic system Over 10.000 new and existing structures: Bridge and viaduct Industrial plants and components Buildings including cultural heritage
