OVERVIEW OF EARTHQUAKE RISK CIVIL ENGINEERING CONTEXT BASIC INFORMATION AND TUTORIALS

The first step in understanding earthquake risk is to dissect the earthquake risk or loss process into its constituent steps. Earthquake risk begins with the occurrence of the earthquake, which results in a number of earthquake hazards.

The most fundamental of these hazards is faulting, that is, the surface expression of the differential movement of blocks of the Earth’s crust. Faulting can be a simple “mole-track” lateral movement, or a major vertical scarp, or may not even be visible.

In most cases, faulting is typically a long narrow feature, and therefore affects a relatively small fraction of the total affected structures and persons. Affecting a much greater number of structures and persons is shaking, which is typically the primary hazard due to earthquakes.

Depending on the earthquake, liquefaction, other forms of ground failure, tsunamis, or other types of hazards may be significant agents of damage. For various reasons, many buildings, portions of the infrastructure, and other structures cannot fully resist these hazards, and sustain some degree of damage.

Primary damage can vary from minor cracking to total collapse. Some building types are more vulnerable than others, but even when a building sustains no structural damage, the contents of the building may be severely damaged.

For certain occupancies, such as hospitals or emergency services dispatch centers, this damage to contents (laboratories, specialized machinery, communication equipment, etc.) can be very important. Additionally, these various kinds of primary damage can lead to other secondary forms of hazard and damage, such as releases of hazardous materials, major fires, or flooding.

Damage results in loss.

Primary loss can take many forms — life loss or injury is the primary concern, but financial loss and loss of function are also of major concern. The likelihood of sustaining a loss is termed risk . Primary losses lead to secondary forms of loss, such as loss of revenues resulting from business interruption and loss of market share and/or reputation.

EARTHQUAKE LOAD CRITERIA SELECTION TUTORIALS

In IBC 2000, the following basic information is required to determine the seismic loads:

1. Seismic Use Group According to the nature of Building Occupancy, each structure is assigned a Seismic Use Group (I, II, or III) and a corresponding Occupancy Importance (I) factor (I = 1.0, 1.25, or 1.5).

Seismic Use Group I structures are those not assigned to either Seismic Use Group II or III. Seismic Use Group II are structures whose failure would result in a substantial public hazard due to occupancy or use.

Seismic Use Group III is assigned to structures for which failure would result in loss of essential facilities required for post-earthquake recovery and those containing substantial quantities of hazardous substances.

2. Site Class Based on the soil properties, the site of building is classified as A, B, C, D, E, or F to reflect the soil-structure interaction. Refer to IBC 2000 for Site Class definition.

3. Spectral Response Accelerations SS and S1 The spectral response seismic design maps reflect seismic hazards on the basis of contours. They provide the maximum considered earthquake spectral response acceleration at short period SS and at 1-second period S1. They are for Site Class B, with 5% of critical damping. Refer to the maps in IBC 2000.

4. Basic Seismic-Force-Resisting System Different types of structural system have different energy-absorbing characteristic. A response modification coefficient R is used to account for these characteristics.

Systems with higher ductility have higher R values. With the above basic parameters available, the following design and analysis criteria can be determined.

ASEISMIC DESIGN OF CIVIL ENGINEERING STRUCTURES BASICS AND TUTORIALS

ASEISMIC DESIGN OF CIVIL ENGINEERING STRUCTURES BASIC INFORMATION
What Are Aseismic Design Of Civil Engineering Structures?


The basic methods for providing wind resistance—shear walls, diagonal bracing, and rigid frames are also suitable for resisting seismic loads. Ductile rigid frames, however, are preferred because of large energy-absorbing capacity.

Building codes encourage their use by permitting them to be designed for smaller seismic loads than those required for shear walls and diagonal bracing. (Ductility is a property that enables a structural member to undergo considerable deformation without failing.

The more a member deforms, the more energy it can absorb and therefore the greater is the resistance it can offer to dynamic loads.) For tall, slender buildings, use of the basic methods alone in limiting drift to an acceptable level may not be cost-effective.

In such cases, improved response to the dynamic loads may be improved by installation of heavy masses near the roof, with their movements restricted by damping devices. Another alternative is installation of energy-absorbing devices at key points in the structural framing, such as at the bearings of bottom columns or the intersections of cross bracing.

Designers usually utilize floors and roofs, acting as horizontal diaphragms, to transmit lateral forces to the resisting structural members. Horizontal bracing, however, may be used instead.

Where openings occur in floors and roofs, for example for floors and elevators, structural framing should be provided around the openings to bypass the lateral forces.

As for wind loads, the weight of the building and of earth adjoining foundations are the only forces available to prevent the horizontal loads from overturning the building. Also, as for wind loads, the roof should be firmly anchored to the superstructure framing, which, in turn, should be securely attached to the foundations.

Furthermore, individual footings, especially pile and caisson footings, should be tied to each other to prevent relative movement. Building codes often limit the drift per story under the equivalent static seismic load.

Connections and intersections of curtain walls and partitions with each other or with the structural framing should allow for a relative movement of at least twice the calculated drift in each story. Such allowances for displacement may be larger than those normally required for dimensional changes caused by temperature variations.

(N. M. Newmark and E. Rosenblueth, ‘‘Fundamentals of Earthquake Engineering,’’ and J. S. Stratta, ‘‘Manual of Seismic Design,’’ Prentice-Hall, Englewood Cliffs, N.J.; ‘‘Standard Building Code,’’ Southern Building Code Congress International, Inc., 900 Montclair Road, Birmingham, AL 35213-1206; ‘‘Uniform Building Code,’’ International Conference of Building Officials, Inc., 5360 South Workman Mill Road, Whittier, CA 90601.)

SEISMIC LOAD ON ROOFS DESIGN AND CALCULATION BASIC AND TUTORIALS

SEISMIC LOAD ON ROOFS DESIGN AND CALCULATION BASIC INFORMATION
How To Make Seismic Load On Roofs Design and Calculation?


Seismic Loads Calculations
The engineering approach to seismic design differs from that for other load types. For live, wind or snow loads, the intent of a structural design is to preclude structural damage. However, to achieve an economical seismic design, codes and standards permit local yielding of a structure during a major earthquake.

Local yielding absorbs energy but results in permanent deformations of structures. Thus seismic design incorporates not only application of anticipated seismic forces but also use of structural details that ensure adequate ductility to absorb the seismic forces without compromising the stability of structures.

Provisions for this are included in the AISC specifications for structural steel for buildings. The forces transmitted by an earthquake to a structure result from vibratory excitation of the ground. The vibration has both vertical and horizontal components.

However, it is customary for building design to neglect the vertical component because most structures have reserve strength in the vertical direction due to gravity-load design requirements. Seismic requirements in building codes and standards attempt to translate the complicated dynamic phenomenon of earthquake force into a simplified equivalent static force to be applied to a structure for design purposes.

For example, ASCE 7-95 stipulates that the total lateral force, or base shear, V (kips) acting in the direction of each of the principal axes of the main structural system should be computed from
V = CsW(9.139)

where Cs seismic response coefficient
W total dead load and applicable portions of other loads

The seismic coefficient, Cs, is determined by the following equation:
Cs = 1.2Cv /RT^2/3(9.140)

where Cv seismic coefficient for acceleration dependent (short period) structures
R response modification factor
T fundamental period, s

Alternatively, Cs need not be greater than
Cs = 2.5Ca/R(9.141)

where Ca seismic coefficient for velocity dependent (intermediate and long period) structures.

A rigorous evaluation of the fundamental elastic period, T, requires consideration of the intensity of loading and the response of the structure to the loading. To expedite design computations, T may be determined by the following:
Ta = CThn^3/4(9.142)

where CT 0.035 for steel frames
CT 0.030 for reinforced concrete frames
CT 0.030 steel eccentrically braced frames
CT 0.020 all other buildings
hn height above the basic to the highest level of the building, ft

For vertical distribution of seismic forces, the lateral force, V, should be distributed over the height of the structure as concentrated loads at each floor level or story. The lateral seismic force, Fx, at any floor level is determined by the following equation:
Fx = CuxV(9.143)

where the vertical distribution factor is given by

(9.144)

where wx and wi height from the base to level x or i
k 1 for building having period of 0.5 s or less 2 for building having period of 2.5 s or more  use linear interpolation for building periods between 0.5 and 2.5 s


For horizontal shear distribution, the seismic design story shear in any story, Vx, is determined by the following:

 (9.145)

where Fi the portion of the seismic base shear induced at level i. The seismic design story shear is to be distributed to the various elements of the force resisting system in a story based on the relative lateral stiffness of the vertical resisting elements and the diaphragm. Provision also should be made in design of structural framing for horizontal torsion, overturning effects, and the building drift.

IMPROVING EARTHQUAKE RESISTANCE OF SMALL BUILDINGS BASICS AND TUTORIALS

IMPROVING EARTHQUAKE RESISTANCE OF SMALL BUILDINGS BASIC INFORMATION
How To Improve The Earthquake Resistance of Small Buildings?


1. Site Selection: 
The building constructions should be avoided on
(a) Near unstable embankments
(b) On sloping ground with columns of different heights
(c) Flood affected areas
(d) On subsoil with marked discontinuity like rock in some portion and soil in some portion.

2. Building Planning: 
Symmetric plans are safer compared to unsymmetric. Hence go for square or rectangular plans rather than L, E, H, T shaped. Rectangular plans should not have length more than twice the width.

3. Foundations:
Width of foundation should not be less than 750 mm for single storey building and not less than 900 mm for storeyed buildings. Depth of foundation should not be less than 1.0 m for soft soil and 0.45 m for rocky ground.

Before foundation is laid remove all loose materials including water from the trench and compact the bottom. After foundation is laid back-fill the foundation properly and compact.

4. Masonry: 
In case of stone masonry:
• Place each stone flat on its broadest face.
• Place length of stones into the thickness of wall to ensure interlocking inside and outside faces of the wall.
• Fill the voids using small chips of the stones with minimum possible mortar.
• Break the stone to make it angular so that it has no rounded face.
• At every 600 to 750 mm distance use through stones.

In case of brick masonry:
• Use properly burnt bricks only.
• Place bricks with its groove mark facing up to ensure better bond with next course.

In case of concrete blocks:
• Place rough faces towards top and bottom to get good bond.
• Blocks should be strong.
• Brush the top and bottom faces before laying.

In general walls of more than 450 mm should be avoided. Length of wall should be restricted to 6 m. Cross walls make the masonry stronger. It is better to build partition walls along main walls interlinking the two.

GEOTECHNICAL EARTHQUAKE ENGINEERING FREE EBOOK DOWNLOAD LINK

GEOTECHNICAL EARTHQUAKE ENGINEERING FREE EBOOK DOWNLOAD
Free E-Book Download Link of the Book: Geotechnical Earthquake Engineering

This is the first book on the market focusing specifically on the topic of geotechnical earthquake engineering. The book draws from the fields of seismology and structural engineering to present a broad, interdiciplinary view of the fundamental concepts in seismology, geotechnical engineering, and structural engineering.


This is the first book on the market focusing specifically on the topic of geotechnical earthquake engineering. The book draws from the fields of seismology and structural engineering to present a broad, interdiciplinary view of the fundamental concepts in seismology, geotechnical engineering, and structural engineering.

One of the few books on geotechnical earthquake engineering. Treatment is extensive though it does not dwell in the specialist details for most topics. The chapter on "Ground response analysis" is excellent. I recently learnt of this professional software, "ProSHKAE" using the theory of this chapter to formulate its algorithm. I relied upon this book for a large part of my undergraduate research.

Yes, this is an excellent overall introduction to the geotechnical aspects of earthquake engineering. We use it regularly in practice. The sections on seismic hazard analysis and seismic slope stability are particularly strong.


Topics in geotechnical earthquake engineering is one of the  most active fields and always in rapid changing. Only with several years off, the book by Professor Kramer is going to  be out-of-dated. Yet it is the BEST book available so far on this topic.

I found the information in this book is useful for learning and understanding, yet for the most excellent descriptions, we have to refer directly to the scattered publications of  Berkeley School (i.e. Prof. H.Seed, R. Seed and J. Bray et al).

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