Proceedings of the International rilem conference Materials, Systems and Structures in Civil Engineering 2016

138

International RILEM Conference on Materials, Systems and Structures in Civil Engineering 

Conference segment on Service Life of Cement-Based Materials and Structures 

22-24 August 2016, Technical University of Denmark, Lyngby, Denmark 

 

These formulae can be used to determine the impact force factor (k

r

), which is based on the 

return periods and consequences of changing operations, such as speeds or wheel/rail defects 

[15]. 

Limit states concept is a more logical entity for use as the design and analysis approach for 

prestressed concrete sleepers, in a similar manner of Australian Standard AS3600 [3]. It 

considers both strength and serviceability. Over time, the concrete sleepers experience diverse 

traffic loads from operational activities, and may have damage and cracks, also resulting in an 

additional time-dependent loss in prestress level [17-19]. However, previous studies have not 

thoroughly investigated the deterioration and residual strength of concrete sleepers [20].  This 

study thus investigates the remaining life of railway prestressed concrete sleepers after a 

period of service life through a variety of structural testing programs. It experimentally 

investigates the remaining service life of railway prestressed concrete sleepers considering 

limit states design concept. The ageing railway concrete sleepers from various operational 

environments have been investigated. This paper presents the nominal reserve capacity of the 

old prestressed concrete sleepers from previous experimental investigations aimed at 

proposing a rational method for evaluating the remaining life of concrete sleepers. 

2.  Limit states of railway concrete sleepers 

According to Leong [15], Australian railway organisations would condemn a sleeper when its 

ability to hold top of line or gauge is lost. It is also found that this practice is actually adopted 

in most of railway industries worldwide. Those two failure conditions can be reached by the 

following actions: 

 

abrasion at the bottom of the sleeper causing loss of top 

 

abrasion at the rail seat location causing a loss of top 

 

severe cracks at the rail seat causing the ‘anchor’ of the fastening system to move and 

spread the gauge 

 

severe cracks at the midspan of the sleeper causing the sleeper to ‘flex’ and spread the gauge 

 

severe degradation of the concrete sleeper due to alkali aggregate reaction or some similar 

degradation of the concrete material. 

 

Since abrasion and alkali aggregate reaction are not structural actions causing failure 

conditions, only severe cracking leading to sleeper’s inability to hold top of line and gauge 

will be considered as the failure criteria defining a limit state related to the operations of a 

railway system. A challenge in the development of a limit states design concept for 

prestressed concrete sleepers is the acceptance levels of the structural performances under 

design load conditions. Infinite fatigue life of sleepers cannot be retained after allowing 

cracks under impact loads. Therefore, the general principles for reliability for structures, and 

indicates that limit states can be divided into the following two categories: 

1.

 

ultimate limit states, which correspond to the maximum load-carrying capacity or, in 

some cases, to the maximum applicable strain or deformation; 

2.

 

serviceability limit state, which concerns the normal use and service life (fatigue and 

deformation). 

 

Leong [15] suggested three limiting conditions would be relevant to the design of railway 

concrete sleeper: 

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139

International RILEM Conference on Materials, Systems and Structures in Civil Engineering 

Conference segment on Service Life of Cement-Based Materials and Structures 

22-24 August 2016, Technical University of Denmark, Lyngby, Denmark 

 

Ultimate Limit State 

A single once-off event such as a severe wheel flat that generates an impulsive load capable 

of failing a single concrete sleeper. Failure under such a severe event would fit within failure 

definitions causing severe cracking at the rail seat or at the midspan. The single once-off 

event will be based on the probabilistic analysis of train load spectrums recorded over several 

years or for a suitable period (generally at least a year as to obtain the good representative of 

track forces over its lifetime under various train/track conditions). The load magnitude of the 

ultimate event for ultimate limit state design of sleepers depends on the significance or 

importance level of the railway track. It should be noted that in some cases when the load 

frequency distributions can only be obtained from the long-term track force measurements, 

the ultimate design loads are usually taken to be the 95 percent fractiles, and hence have a 5 

percent probability of being exceeded [19]. 

 

Damageability (or Fatigue) Limit State 

A time-dependent limit state where a single concrete sleeper accumulates damage 

progressively over a period of years to a point where it is considered to have reached failure.  

Such failure could come about from excessive accumulated abrasion or from cracking having 

grown progressively more severe under repeated loading impact forces over its lifetime. In 

sleeper design perspective, the lifetime can be specified by the design service life of the 

sleepers (e.g. 30, 50, or 100 years) or from the expected train/track tonnage (or how many 

load cycles expected for the track infrastructure, e.g. 10, 50, or 100 million cycles). The 

loading ranges for the fatigue life prediction vary on the load frequency distribution as shown 

in Figure 2 (the load frequency data recorded for a year). Using the data in Figure 2 for 

fatigue life prediction of sleepers is applicable whereas the actual life must be longer than 

design life. Alternatively, if the sleeper is to be designed for 50 year service life under 28ton 

axle load, the loading range for the fatigue life consideration can be obtained from Equation 1 

plus the wheel load of 140kN, which is up to 540 kN [15]. Using a statistical analysis, the 

number of axles or cycles of each loading range can be achieved for the cumulative fatigue 

damage. Based on previous example, it shows likelihood that there is only 1 time that the 

sleeper experiences the dynamic load of 540 kN over the sleeper design life of 50 years. Once 

the numbers of cycle in each loading range (e.g. 105-115 kN, 535-545 kN range) are 

obtained, the cumulative fatigue damage can be calculated using the endurance limits of 

materials or generic fatigue design codes (e.g. European Code, CEB Model code, etc.). Such 

damage should not result in any failure condition described earlier. 

 

Serviceability Limit State 

This limit state defines a condition where sleeper failure is beginning to impose some 

restrictions or tolerances on the operational capacity of the track, for example, prestressing 

losses, sleeper deformations (shortening and camber), track stiffness, etc.  The failure of a 

single sleeper (in track system) is rarely if ever a cause of a speed restriction or a line closure.  

However, when there is failure of a cluster of sleepers, an operational restriction is usually 

applied until the problem is rectified. Recently, this serviceability limit state has extensively 

applied to the methodology for retrofit and replacement of sleepers made of different material 

properties in the existing aged track systems. For example, the deteriorated timber sleeper 

tracks have been replaced by new concrete/steel sleepers through a suitable spacing 

arrangement as to provide a similar track modulus or stiffness to the existing one. This 

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