Permissible flexural stresses in tendons and concrete according to ACI

PERMISSIBLE FLEXURAL STRESSES IN TENDONS & CONCRETE ACCORDING TO ACI CODE : 

PERMISSIBLE FLEXURAL STRESSES IN TENDONS & CONCRETE ACCORDING TO ACI CODE PRESENTED BY TATHEER AKHLAQ 2006-MSC-CIVIL-STRU-08

Introduction : 

Introduction Most specifications for prestress concrete construction impose certain limitations on stresses in the concrete and steel at particular stages Stages:- While tensioning the steel, immediately after transfer of prestress force to the concrete. At full service load.

Introduction : 

Introduction These stress limits are intended to avoid damage to the member during construction, and to insure servicibilty by indirectly limiting crack width and deflection. The resulting design must be checked for strength to ensure adequate safety agianst failure. Often deflections must also be calculated explicitily at particular load stages of importance.

PERMISSIBLE STRESS IN CONCRETE : 

PERMISSIBLE STRESS IN CONCRETE

Permissible Stresses In Concrete : 

Permissible Stresses In Concrete Concrete stress limits imposed by the ACI are summarized in the tables given below. Here Fci’ = compressive strength of the concrete at the time of initial pretress Fc’ = specified compressive strength of the concrete

Stage 1: Permissible Stresses After Transfer Of Prestress Force : 

Stage 1: Permissible Stresses After Transfer Of Prestress Force The allowable stresses of Table 1 apply immediately after Transfer of prestress force to the concrete Loss due to friction Anchorage slip Elastic shortening of the concrete have been deducted But before time-dependent losses due to shrinkage, creep and relaxation are taken into account.

Table 1Permissible Stresses After Transfer Of Prestress Force : 

Table 1Permissible Stresses After Transfer Of Prestress Force

Stage 2: Service Load Stress Limit : 

Stage 2: Service Load Stress Limit The service load stress limits apply after all losses have occurred and when the full service load acts.

Table 2: Service Load Stress Limit : 

Table 2: Service Load Stress Limit

Stage 3: Escape Clause : 

Stage 3: Escape Clause The “ escape clause” permits higher stresses to be used when tests or analysis indicate that satisfactory performance can be expected. The permissible stresses of table 1 and 2 may be exceeded if shown by test or analysis that performance will not be impaired.

PERMISSIBLE STRESSES IN STEEL : 

PERMISSIBLE STRESSES IN STEEL

Permissible Stresses In Steel : 

Permissible Stresses In Steel The permissible stresses in steel are given in table 3. Here Fpu= Ultimate strength of the steel Fpy = Specified yield strength of steel

Table 3:Permissible Stresses In Steel : 

Table 3:Permissible Stresses In Steel

Slide 14: 

The code commentry warns that designers should be concerned with setting a limit on final stress when structure is subjected to corrosive condition and repeated load.

THANKS : 

THANKS