Close Menu
  • About Us
  • Services
    • House Plans/Views
    • Books
    • Videos
    • Softwares/Programmes
    • Job/Scholarship Adverts
  • Notes
    • Structural Engineering
    • Surveying
    • Geotechnical Engineering
    • Design Codes
    • Highway/Transportation Engineering
    • Environmental Engineering
    • Concrete Technology
    • Soil Mechanics
    • Mathematics
    • Strength of Materials
    • Fluid Mechanics and Hydraulics
    • Water Resources Engineering
  • Quiz
  • Privacy Policy
  • Terms and Conditions
  • Q&A
  • About Us
  • Services
    • House Plans/Views
    • Books
    • Videos
    • Softwares/Programmes
    • Job/Scholarship Adverts
  • Notes
    • Structural Engineering
    • Surveying
    • Geotechnical Engineering
    • Design Codes
    • Highway/Transportation Engineering
    • Environmental Engineering
    • Concrete Technology
    • Soil Mechanics
    • Mathematics
    • Strength of Materials
    • Fluid Mechanics and Hydraulics
    • Water Resources Engineering
  • Quiz
  • Privacy Policy
  • Terms and Conditions
  • Q&A
  • en
    • ar
    • zh-CN
    • nl
    • en
    • fr
    • de
    • it
    • pt
    • ru
    • es
Facebook X (Twitter) Instagram YouTube LinkedIn WhatsApp
Home»Structures»Seismic Design of Buildings | Special Considerations
Structures

Seismic Design of Buildings | Special Considerations

Mezie EthelbertBy Mezie EthelbertUpdated:
Facebook Twitter LinkedIn Telegram WhatsApp Pinterest Email Copy Link
Share
Facebook Twitter LinkedIn Pinterest Email Reddit Telegram WhatsApp
Reading Time: 3 minutes

The single most important seeming principle in seismic design is to ensure that the structural components and systems are adequately tied together to perform as a structural unit. However, due to uncertainties surrounding how a sturdy structural system can be achieved, other special considerations are applied in the seismic design to guard against failure.  These considerations include:

Table of Contents

  • Over Strength
  • Redundancy Factor
  • Deflection Amplification
  • Irregularities
  • Deformation Compatibility

Over Strength

The concept of overstrength is a realization that a shear-resisting system’s ultimate capacity is usually significantly higher than required by a design load as a result of intended safety margins. At the same time, the seismic ground motion (load) is reduced by the seismic response modifier factor (R-factor) to account for the ductile response of the building system, among other things. Thus, the actual forces experienced on various components (i.e. connections) during a design-level event can be substantially higher, even though the resisting system may be able to effectively dissipate that force. Therefore, over-strength factors have been included in newer seismic codes with recommendations to assist in designing components that may experience higher forces than determined otherwise for the building lateral force-resisting system. In essence, the over-strength concept is an attempt to address the principle of balanced design. It strives to ensure that critical components, such as connections, have sufficient capacity so that the overall lateral force-resisting system is able to act in its intended ductile manner (i.e., absorbing higher-than-design forces). Thus, a premature failure of a critical component (i.e., a restraining connection failure) is avoided. This requires adequate designer judgment in addition to code requirements.

Redundancy Factor

This was postulated to address the reliability of lateral force-resisting systems by encouraging multiple lines of shear resistance in a building. Redundancy is an area where exact guidance does not exist and the designer must exercise reasonable care in accordance with or in addition to the applicable building code requirements.

Deflection Amplification

Deflection amplification has been applied in past and current seismic design codes to adjust the deflection or story drift determined by the use of the design seismic shear load (as adjusted downward by the R-factor) relative to that actually experienced without allowance for modified response (i.e., load not adjusted down by the R-factor). This often requires multiplying the value of seismic shear load, V by a factor, and the situation is onerous based on the susceptibility of the building to collapse. This application also requires designer judgment.

Irregularities

Irregularities are related to special geometric or structural conditions that affect the seismic performance of a building and either require special design attention or should be altogether avoided. In essence, the presence of limits on structural irregularity speaks indirectly of the inability to predict the performance of a structure in a reliable, self-limiting fashion on the basis of analysis alone. Therefore, many of the irregularity limitations are based on judgment from problems experienced in past seismic events.

Irregularities are generally separated into plan and vertical structural irregularities. Plan structural irregularities include torsional imbalances that result in excessive rotation of the building, re-entrant corners creating “wings” of a building, floor or roof diaphragms with large openings or non-uniform stiffness, out-of-plane offsets in the lateral force resistance path, and non-parallel resisting systems. Vertical structural irregularities include stiffness irregularities (i.e., a “soft” storey), capacity irregularities (i.e., a “weak” storey), weight (mass) irregularity (i.e., a “heavy” storey), and geometric discontinuities affecting the interaction of lateral resisting systems on adjacent storeys.

The concept of irregularities is associated with ensuring an adequate load path and limiting undesirable (i.e., hard to control or predict) building responses in a seismic event. Again, experienced designers generally understand the effect of irregularities and effectively address or avoid them on a case-by-case basis. For typical single-family housing, all but the most serious irregularities (i.e., “soft storey”) are generally of limited consequence, particularly given the apparently significant system behavior of light-frame homes (provided the structure is reasonably “tied together as a structural unit”). For larger structures, such as low and high-rise commercial and residential construction, the issue of irregularity and loads becomes more significant. Because structural irregularities raise serious concerns and have been associated with building failures or performance problems in past seismic events, the designer must exercise reasonable care in accordance with or in addition to the applicable building code requirements.

Deformation Compatibility

This issue may be handled through the specification of materials that have similar deformation capabilities or by system detailing that improves compatibility. For example, a relatively flexible hold-down device installed near a rigid sill anchor causes greater stress concentration on the more rigid element. The solution can involve increasing the rigidity of the hold-down device (which can lessen the ductility of the system, increase stiffness, and effectively increase seismic load) or redesigning the sill plate connection to accommodate the hold-down deformation and improve load distribution. There is little definitive design guidance on deformation compatibility considerations in the seismic design of wood-framed buildings and other structures. The designer’s judgment may also be applicable here.

Source

ACI-318 (Residential Structural Design Guide), Chapter 3: Design Loads for Residential Buildings

Share this:

  • Click to share on Facebook (Opens in new window) Facebook
  • Click to share on X (Opens in new window) X

Related

buildings compatibility deflection earthquakes redundancy seismic
Share. Facebook Twitter Pinterest LinkedIn Email Telegram WhatsApp Copy Link
Previous ArticleHow to Determine Soil Bearing Capacity and Footing Size according to ACI-318
Next Article Effect of Shape on the Lateral Resistance of Tall Buildings
Mezie Ethelbert

An inquisitive engineer with considerable skills in analysis, design and research in the field of civil engineering.

Related Posts

Important Tests Required in Tunnel Construction

How to Check Shear for Pad Footings according to EC 7

General Causes and Remedies to Building Collapse

Add A Comment

Leave a ReplyCancel reply

May 2025
M T W T F S S
 1234
567891011
12131415161718
19202122232425
262728293031  
« Dec    
INTRO VIDEO OF OUR SERVICES
https://mycivillinks.com/wp-content/uploads/2022/01/Lemarg-Consulting-Services-Intro-Video.mp4
CLICK ON THE BOOK COVER TO SEE CONTENT
theory of structures
CLICK ON THE BOOK COVER TO SEE CONTENT
BLOG SUBSCRIPTION

Get the latest posts on this blog

MOST RECENT POSTS

Common Rules of Thumb in Geotechnical Engineering

Important Tests Required in Tunnel Construction

Concise Notes on Bearing Capacity and Settlement of Soils (PDF)

MOST VIEWED POSTS
  1. Differences between University and Polytechnic Education System in Nigeria (Example of Civil Engineering Syllabus) (9,964)
  2. COREN Past Interview Questions for different Engineering Divisions in Nigeria (8,037)
  3. Standard Rules for Setbacks in Nigeria for Structures (8,032)
  4. COREN professional interview (COREN P.I.) (7,555)
  5. Structural Analysis and Design of Sawtooth or Slabless Staircase (7,241)
  6. Analysis and Design of Sheet Piles (PDF) (6,824)
POSTS CATEGORIES
© {2025} Mycivillinks. All rights reserved
  • About Us
  • Services
    • House Plans/Views
    • Books
    • Videos
    • Softwares/Programmes
    • Job/Scholarship Adverts
  • Notes
    • Structural Engineering
    • Surveying
    • Geotechnical Engineering
    • Design Codes
    • Highway/Transportation Engineering
    • Environmental Engineering
    • Concrete Technology
    • Soil Mechanics
    • Mathematics
    • Strength of Materials
    • Fluid Mechanics and Hydraulics
    • Water Resources Engineering
  • Quiz
  • Privacy Policy
  • Terms and Conditions
  • Q&A

Type above and press Enter to search. Press Esc to cancel.