Page 51 - EQTips_Eng

IITK-BMTPC Earthquake Tip 25

Why are Load Paths Important in Buildings? page 2
Horizontal floors can effectively resist and transfer (b) Load path geometry must be simple: Uninterrupted,
earthquake forces through direct load paths, provided direct load paths should be provided at regular
that they do not have significant openings. Large intervals along length and width of the building;
openings or cut-outs in floors interrupt load paths and (c) Load paths must be symmetrical in plan: A building
may prevent smooth, direct transfer of forces to will sway uniformly in two horizontal directions,
vertical elements. Openings in floors are necessary, when structural elements constituting load paths
e.g., to allow for elevator core or staircase to pass are placed symmetrically in plan. Otherwise, it may
through. But, these should be as small as possible, and twist about a vertical axis, which is detrimental to
as few as possible. Their locations should be carefully its earthquake performance.
considered; the ideal location for openings is close to (d) Robust connections are needed between structural
center of floor slabs in plan. elements along load paths: In an earthquake-resistant
Vertical Elements structure, every connection is tested during strong
Typical structural elements (present in vertical earthquake shaking. These connections should be
planes) of buildings are columns, braces and structural stiff and strong to offer continuous load paths
walls or a combination of these (Figure 3). They collect without being damaged during strong earthquake
gravity and (horizontal and vertical) earthquake inertia shaking (Figure 4).
forces from floor diaphragms at different levels, and
bring them down to the foundations below.
It is possible to design and construct earthquake-
resistant buildings with various structural systems,
including Moment Resisting Frames (MRFs), Frames
with Brace Members (called Braced Frames (BFs)),
Structural Walls (SWs; also called Shear Walls), or a
combination of these. Some of these systems require
more advanced knowledge of design and higher
quality control during construction than others, as
reflected by their relative performance during
earthquakes. For instance, buildings with SWs are easy
to design and construct, and generally perform better
during earthquakes, than buildings with MRFs alone.

Photo Courtesy: Sudhir K. Jain

Figure 4: Deficient connection between slabs
and vertical elements – collapse of an RC
frame building during 2001 Bhuj (India)

earthquake

(a) (b) (c) Related - Earthquake Tip

Figure 3: Structural systems in buildings that Tip 5: What are seismic effects on structures?
Tip 6: How architectural features affect buildings during
help resist lateral earthquake-induced inertia earthquakes?
loads – (a) MRFs : moment-resisting frames,

(b) BFs : braced frames, and (c) frame-wall dual
systems Resource Material
Arnold,C., and Reitherman,R., (1982), Building Configuration and
Seismic Design, John Wiley, USA
Key Requirements of Load Paths Ambrose,J., and Vergun,D., (1999), Design for Earthquakes, John
Earthquake performances of buildings are Wiley & Sons, Inc., USA
determined by soundness of their load paths,

independent of the material with which buildings are
built, e.g., masonry, RC or structural steel. Earthquake Authored by:
codes require designers to ensure presence of adequate C.V.R.Murty

lateral load paths in buildings in two horizontal plan Indian Institute of Technology Jodhpur, India
directions. Salient requirements of load paths are: Sponsored by:
(a) Load paths must exist in all directions of a building: Building Materials and Technology Promotion

Earthquake shaking occurs in all directions, and Council, New Delhi, India
can be expressed as a combination of shaking in
one vertical and two (mutually perpendicular) This release is a property of IIT Kanpur and BMTPC. It may

horizontal directions. Hence, adequate load paths be reproduced without changing its contents with due
acknowledgement. Suggestions or comments may be sent
are needed along the vertical and the two mutually to: nicee@iitk.ac.in. To see all IITK-BMTPC Earthquake Tips, visit
perpendicular horizontal directions. www.nicee.org or www.bmtpc.org.