Resources for Civil & Structural Engineers
Members Login
mec
engineers
FREE Engineering Articles
Home About Us Services Jobs Post-It Contact Us
 

Sign Conventions for Prestressed Concrete Design

In design of Prestressed Concrete, the most commonly used equations are related to stresses for sectional properties of Precast Concrete Sections and Composite Sections. The equations very simple to understand and use, however, many found confusion when loadings become complex and other factors such as losses, transfer, service and ultimate loads are included and especially when sectional properties change.

Inorder to ensure continuity of a complex series of equations, it is important to maintain very strict use of Sign Conventions, without which all your calculations for stresses will be mixed up and wrong.

For any Sectional Properties the following are normally used :-

A = Area of Concrete
P = Prestressing Force
e = eccentricity of Prestressing Force from Centroid of Section
M = Moment due to External Loads (such as beam self weight, dead loads, service loads)
Zt= Second Moment of Area (Top Section)
Zb= Second Moment of Area (Bottom Section)
ft = Stress at Top Fibre (sigma sign normally used-refer calc sheet)
fb = Stress at Bottom Fibre (sigma sign normally used-refer calc sheet)

Sign Convention Used :-

M = -ve if HOGGING, +ve if SAGGING
e = -ve if Bottom of Centroid, +ve if Top of Centroid
Z = -ve if Bottom of Centroid, +ve if Top of Centroid

(f & P = -ve if tensile, +ve if compressive)

Stress " f " in any Concrete Sections is given by the Equation :-

f = P/A + Pe/Z + M/Z

(e, M, Z,  can be -ve or +ve using the sign convention)

The above is illustrated in a simple calculation below :-

 Sign Conventions for Prestressed Concrete 

We welcome all comments and enquiries- Contact Us. Subscribe to our Free Newsletters on Engineering Designs

 

Authur- Philip Goh (B.Sc, MIEM, P.Eng. MICE, C.Eng)
MEC Engineers, Civil & Structural Engineer
Email:   

 

 

 

 

To Order
Design EBooks
Contact Us

 
 Calculations & Worked Examples for Design of Drainage System.

 Drainage Calcs

 Calculations for Design of Water Reticulation System

 Water Supply

 Calculations for Design of Circular RC Water Tanks

RC Water Tanks

-----------------

 

Authur- Philip Goh (B.Sc, MIEM, P.Eng. MICE, C.Eng) MEC Engineers, Civil & Structural Engineer HP: 016-8672189, Email: Widget: email cloaker