Page 137 - Handbook of Materials Failure Analysis

4 Current Analysis and Design Methods 133

−26kNm

+40kNm

500 mm 1800−4200 mm 500 mm

85kN

Bending moment envelope and
shear force envelope
FIGURE 6.7
Shear force and bending moment envelopes for bearer lengths 2.8-5.2 m.

4.1 METHODS OF ANALYSIS

Actual contact pressure distribution in sleepers and bearers varies over time, making it
virtually impossible to predict the exact conditions in actual conditions. Various
hypothetical contact pressure distributions are shown in Figure 6.9.In Figure 6.10,
the effect of the modulus (K s ) of ballast shows that the stiffer the sleeper support (the
ballast), the more localized the contact stresseswill be. Further, in Figure 6.11, the more
flexible the sleeper is, again the more localized the contact stress will be.
4.1.1 Determination of rail seat load
The magnitude of the load applied to the sleepers from the rail depends on these
known and unknown figures:
(i) the rail weight;
(ii) the sleeper spacing;
(iii) the sleeper stiffness characteristics;
(iv) the track modulus per rail;
(v) pad stiffness;