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CE100Introduction to

Civil Engineering

Structural Engineering

Dr. Talat A Bader

Lecture 4

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Outline

• Objective of Structural Engineering• Structural Engineering Process• Types of loads• Types of structures• Load paths in structures• Summary

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Civil EngineeringSub-disciplines @KFUPM

• Structural• Geotechnical• Transportation• Water

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Objectives of Structural Engineering

Structural engineering is the science and art of designing and making, with economy and elegance, buildings, bridges, frameworks, and other structures so that they can safely resist the forces to which they may be subjected.

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Structural Engineering Process

• Determine types magnitudes of loads• Determine structural context

• geometric and geological information• cost / schedule / height/ etc. limitations

• Generate alternative structural systems• Analyze one or more alternatives• Select and perform detailed design • Implement (usually done by contractor)

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Types of loads

• Dead loads• Live loads • Dynamic loads (e.g., trains, equipment)• Wind loads• Earthquake loads• Thermal loads• Settlement loads

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Dead Loads

• weight of the structure itself• floors, beams, roofs, decks, beams/stringers,

superstructure• loads that are “always there”

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Live Loads

• People, furniture, equipment

• Loads that may move or change mass or weight

• Minimum design loadings are usually specified in the building code

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Load Example: Live Load in Ballroom

Live Load = 100 lb/ft^2Wedding Ballroom

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Sears Tower – Chicago IL

• 443 meters - high - & 520 meters - including twin antenna towers. • The Skydeck is 412 meters above the ground. • The lowest level is 13 meters below the Franklin St. elevation. • The combined weight of the building is 222,500tons - or 201,849,000kg. • The cost of building in excess of $150 million. • The was opened in 1973, took 3 years to build. • The building has 418,064 gross square meters of floor space. • Visibility from the Skydeck is approximately 65 - 80 kilometers. • The average sway of the building is appox. 152 millimeters from true center. • Has approximately 16,100 bronze-tinted windows. • 6 roof-mounted robotic window washing machines clean all 16,100 windows. • Elevators operate as fast as 488 meters per minute.• The Tower contains 3,220 kilometers of electrical cable. • The Tower contains Approx. 69,200 kilometers of telephone cable.• The Sears Tower was designed for more than 12,000 occupants. • Approximately 25,000 people enter the building each day. • Approximately 1.5 million tourists visit the Skydeck each year.

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Structural Engineering - Example

• Overturning moment• Overturning moment = (area)(force/area)(moment arm) = (1450 ft x

178 ft)(60 lb/ft2)(725 ft) = 5.6 million ton-ft• Resisting moment

• Resisting moment = force x moment arm = 150,000 tons x 84 ft = 12.6 million ton-ft

• But… soil must be strong!

1450 ft

150-225 ft

60 lb/ft2150,000 tons

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Dynamic Loads

• Moving loads (e.g. traffic)• Impact loads• Gusts of wind• Loads due to cycling

machinery

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Load Example: Dynamic Load

HVAC

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Load Example: Water in a dam

Water,ρ = density

hp = ρgh

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Earthquake Loads

• Structure loaded when base is shaken• Response of structure is dependent on the

frequency of motion• When frequencies match with natural

frequency of structure - resonance

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Load Example: Earthquake Load

Base Motion

Earthquake Load

Earthquake Load

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Earthquake Examples

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Some Types of Structures

• Arch• Planar Truss• Beam/Girder• Braced Frame• Rigid Frame• Space Truss• Cable Suspended Structure

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Arch

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Arch Bridge Dr

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Different types of arch bridge configurations

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Examples Dr

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Planar Truss

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Samples of Common Trusses used in Bridge Construction

Warren Truss Howe Truss

Pratt Truss

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Beam Bridge

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Cable Suspended Structure Dr

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Cantilever Bridge Dr

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Cable Stayed Bridges

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Cable Stayed Bridge Dr

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Beam/Girder

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Examples Dr

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FramesBraced Rigid

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Examples Dr

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Load Paths in Structures

• Load Path is the term used to describe the path by which loads are transmitted to the foundations

• Different structures have different load paths

• Some structures have only one path• Some have several (redundancy good)

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Load Path in Framed StructureDr

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Summary

• Structural Engineering:• identifies loads to be resisted• identifies alternatives for providing load

paths (arch, truss, frame, ...)• designs structure to provide safe and

economical load paths (material, size, connections)

• to be economical and safe, we must be able to predict what forces are in structure.

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Structural Core & Elective

Structural Engineering - Core• CE 201 Statics (3-0-3)• CE 203 Structural Mechanics I (3-0-3)• CE 305 Structural Analysis I (3-0-3)• CE 315 Reinforced Concrete I (2-3-3)• CE 420 Construction Engineering (3-0-3)

Structural Engineering - Electives• CE 405 Structural Analysis II (3-0-3)• CE 406 Structural Mechanics II (3-0-3)• CE 408 Steel Design I (2-3-3)• CE 415 Reinforced Concrete II (2-3-3)• CE 417 Reinforced Concrete III (3-0-3)• CE 418 Steel Design II (3-0-3)

Material Engineering - Core• CE 303 Structural Materials (3-3-4)

Material Engineering - Electives• CE 401 Concrete Technology (2-3-3)• CE 402 Durability, Evaluation and Repair of Concrete Structures (3-0-3)