• 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
Facebook Twitter Instagram YouTube LinkedIn WhatsApp
Home»Building»Factors that affect Deflection in Structural Members
Building

Factors that affect Deflection in Structural Members

Mezie EthelbertBy Mezie EthelbertUpdated:No Comments
Image Source (The Structural Guide-www.structuralguide.com)
Image Source (The Structural Guide-www.structuralguide.com)
Share
Facebook Twitter LinkedIn Pinterest Email Reddit Telegram WhatsApp
Reading Time: 3 minutes

The following factor usually affect deflection in structural members (especially concrete)

Table of Contents

  • Tensile Strength
  • Creep
  • Elastic Modulus
  • Loading Sequence
  • Cracking
  • Shrinkage Curvature

Tensile Strength

This property is important because the slab will crack when the tensile stress in the extreme fibre is exceeded. In Eurocode, the concrete tensile strength, fctm is a mean value used for deflection calculations and which increases with compressive strength. The effective tensile strength of concrete depends on the degree of restraint to shrinkage movements which in turn depends on wall layout.

Creep

This is the time-dependent increase in compressive strain in a concrete element under constant compressive stress. Creep is usually considered in the design by modifying the elastic modulus using a creep coefficient, which depends on the age of loading, size of the member, and ambient conditions. In the assessment of creep, the cement strength is taken into consideration. Generally, Class R should be assumed. Class N should be assumed where the ground granulated blast furnace slag (ggbs) content exceeds 35% of the cement combination or where fly ash (pfa) exceeds 20% of the cement combination. Class S may be assumed where ggbs exceeds 65% or where pfa exceeds 35%.

Elastic Modulus

The elastic modulus is influenced by the aggregate type, workmanship, and curing conditions. The effective elastic modulus under sustained loading will be reduced over time due to the effect of creep. The long-term elastic modulus often used in the calculation should be taken as;
Ec,lt = Ec28/ (1 + φ)

Where,
Ec28 = 28-day tangent modulus = 1.05 Ecm where Ecm is the 28-day secant modulus (Table 3.1 (Strength and Deformation Characteristics for Concrete) of EC 2 gives recommended values-see attached)
φ = the creep factor

Loading Sequence

The loading sequence of the suspended slab will influence the point at which the slab will crack and is used in calculating creep. The loading sequence generally depends on the construction method. After construction, slabs that have experienced temporary loading at the stage of construction will be permanently loaded with finishes and partitions, and variable actions. EC 2 recommends the use of a quasi-permanent combination for deflection calculation associated with the loading sequences.

Cracking

A slab undergoing deflection and a visible deflection must have exceeded its cracking capacity. The point at which cracking occurs is determined by the moments induced in the slab and the tensile strength of the concrete, which increases with age. The critical situation usually occurs when the slab is struck or when the load of the slab above is applied. Once the slab cracks, its stiffness is permanently reduced. Hence, it becomes necessary to find the critical loading stage at which cracking first occurs.

The critical loading stage corresponds with the minimum value of k,

Where,
k = fctm/ (w√0.5)

Where,
w = the serviceability loading applied up to that stage
fctm = the concrete tensile strength at that stage

Shrinkage Curvature

Shrinkage depends on the water/cement ratio, relative humidity, and the size and shape of the member. The effect of shrinkage in an asymmetrically reinforced section is to induce a curvature that can lead to significant deflection in shallow members. This effect should be considered in the deflection calculations.

Source
Bond, A.J., Harrison, T., Narayanan, R.S.; Brooker, O., Moss, R.M., Webster, R. and Harris, A.J. (2006). How to design concrete structures using Eurocode 2. The Concrete centre, UK

Previous ArticleEffect of Shape on the Lateral Resistance of Tall Buildings
Next Article How to determine Earthquake Loads on Low-rise light-frame buildings according to ACI-318
Mezie Ethelbert

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

Related Posts

Methods of Analysis of Trusses

Determination of Permanent Actions and Imposed Loads for Structural Design of Buildings according to EC 2

Measures to Prevent Fire Incidence in Buildings

Add A Comment

Comments are closed.

We have got you covered!
  • 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

CATEGORIES

  • Architecture (1)
  • Bridge (4)
  • Building (5)
  • Codes (2)
  • Construction (42)
  • Cost Engineering (1)
  • Designs (3)
  • Education (6)
  • Engineering Bodies (2)
  • Engineering Science (5)
  • Fire (1)
  • Geotechnical Laboratory Tests (1)
  • Geotechnics (52)
  • Highway Engineering (29)
  • Informative Posts (8)
  • Mechanical (1)
  • News (4)
  • Project Management (13)
  • Real Esate (3)
  • Research (1)
  • Safety (2)
  • Soil Classification (1)
  • Structures (32)
  • Transportation Engineering (1)
  • Water Engineering (8)
To see the Book Content, Click HERE. To BUY THE BOOK, CLICK ON THE COVER
Passionate to Build Your Skillset in Architecture, Engineering and Construction, Click the Image Below:
LATEST POSTS

Methods of Analysis of Trusses

Minimum Superimposed Floor Loads on Buildings and other Simple Structures according to Nigeria Code of Practice (NCP 1: 1973)

Determination of Permanent Actions and Imposed Loads for Structural Design of Buildings according to EC 2

How to Know the Suitable Method to use to determine the Subgrade CBR in Pavement Construction

MOST VIEWED POSTS
  1. Differences between University and Polytechnic Education System in Nigeria (case study of Civil Engineering)
  2. Structural Analysis and Design of Sawtooth or Slabless Staircase
  3. COREN professional interview (COREN P.I.)
  4. Similarities and Differences between AASHTO and USCS soil classification systems
© {2021} 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.