Structure Fatigue in Building


Structure Fatigue in Building

Fatigue life analysis is a method used to calculate the risk of damage due to repeated loads and the age of a structure. The fatigue life of the structure is the number of cycles of cyclic stress that occur before the steel fails (fatigue failure). The cyclic stresses are divided into three types, namely:

  1. Fully reversed
  2. Repeated
  3. Fluctuating

In bridges, the type of cyclic stress that generally occurs is fluctuating cyclical stress. The loading parameters that affect the fatigue of the steel structure are the average stress (σm), the amplitude stress (σa), the ultimate stress (σu), and fatigue limit stress (σe). 

An example of a cyclic (repetitive) load is a traffic load which can significantly reduce the strength and service life of a structure. Therefore, in planning a bridge structure, it is necessary to conduct an in-depth study of the actual load of vehicle traffic to be borne by the structure so that the utilization of the bridge structure can be optimized. 

The traffic load consists of uniform loads as well as line loads and truck loads whose magnitude is influenced by the shock factor (dynamic load allowance). This traffic load is repetitive (cyclic) with a repetition factor according to the Average Daily Rate (LHR).


Main Problem

The fatigue factor of the material due to repeated loads can also cause a degradation of the strength of the material, although the load is still much smaller than the capacity of the structure. Structural fatigue is caused by cyclic loading. Cyclic loads cause stresses on the structure so that cyclic stresses occur.

Increasing the frequency of cyclic loads will cause a decrease in the fatigue life of the structure so that the service life of the bridge becomes shorter. Signs of structural damage due to cyclic loading, namely brittle fracture, wear, cracks and loss of concrete, deflection of beams, and slabs.



  • In planning a bridge, the planner needs to review the average Daily Cross development level of a bridge. This review is necessary so that the bridge can be designed with a strength capable of carrying traffic loads until the end of the design life. 
  • On bridges where the Average Daily Cross is not recorded or cannot be predicted, periodic physical reviews should be carried out along with observations of the actual fatigue life of the structure to prevent unexpected structural failures.
  • On bridges that have been damaged due to the influence of cyclic loads which cause a decrease in the capacity of the existing structure, it is necessary to repair and strengthen the structure. Several methods of repairing concrete surfaces (repair concrete) that can be done include:
    • Injection, for crack repair by injection of epoxy resin.
    • Patching, for repairing small-scale chipped surfaces by hand.
    • Grouting, for repairing lumpy surfaces on a large scale using a pump.
    • Reinforcement of slab structures, girders, and bridge piers with FRP (CFRP/GFRP) with tyfo S for dry structural areas and tyfo SW for wet or flooded areas.



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