Novel Bending Test Method for Polymer Railway Sleeper Materials

Abstract

Alternative sleeper technologies have been developed to address the significant need for the replacement of deteriorating timber railway sleepers. The review of the literature indicates that the railway sleepers might fail while in service, despite passing the evaluation tests of the current composite sleeper standards which indicated that these tests do not represent in situ sleeper on ballast. In this research, a new five-point bending test is developed to evaluate the flexural behaviour of timber replacement sleeper technologies supported by ballast. Due to the simplicity, acceptance level of evaluation accuracy and the lack of in-service behaviour of alternative sleepers, this new testing method is justified with the bending behaviour according to the Beam on Elastic Foundation theory. Three timber replacement sleeper technologies—plastic, synthetic composites and low-profile prestressed concrete sleepers in addition to timber sleepers—were tested under service loading condition to evaluate the suitability of the new test method. To address the differences in the bending of the sleepers due to their different modulus of elasticities, the most appropriate material for the middle support was also determined. Analytical equations of the bending moments with and without middle support settlement were also developed. The results showed that the five-point static bending test could induce the positive and negative bending moments experienced by railway sleepers under a train wheel load. It was also found that with the proposed testing spans, steel-EPDM rubber is the most suitable configuration for low bending modulus sleepers such as plastic, steel-neoprene for medium modulus polymer sleepers and steel-steel for very high modulus sleepers such as concrete. Finally, the proposed bending moment equations can precisely predict the flexural behaviour of alternative sleepers under the five-point bending test.

Yeni LCR Tipi Traverslerin Demiryolu Hat Rijitliğine Etkisinin Araştırılması

“…Örnek olarak AREMA normu (Chapter 30-35) bu alternatif traverslerin elastisite modülünün en az 1,17 GPa olmasını isterken, Japon standartları (JIS E 1203:2007) 6 GPa minimum değerini vermekte, yeni Avustralya standardı (AS1085.22:2020) ise herhangi bir elastisite modülü belirtmemektedir. ISO 12856 standardı ise 1,17 GPa ile 6 Gpa şartlarına haiz 3 kategorili bir yöntem sunmaktadır [41].…”

“…Traverslerin elastisite modülleri ve kütleleri ise, hat rijitliğini ve tüm demiryolu sisteminin davranışını etkilemektedir ve gerek hat rijitliği açısından gerekse Şekil 1'de izah edilen yüksek etki hızlı dinamik yüklere dayanımı açısından büyük öneme sahiptir [39]. Birçok farklı travers üzerinde yapılan test ve analizler sonucunda, traverslerin eğilme modüllerinin, balast modülünden dahi önemli olduğu ve ray mesnedindeki eğilme momentinin (sagging), travers merkezindeki eğilme momentine (hogging) oranının, travers modülü gereğinden fazla yüksek veya düşük olması halinde arttığı belirlenmiştir [41]. Dolayısıyla yüksek servis ömrü ve performans için traverslerin optimum elastisite modülüne ve yeterli yüksek kütleye sahip olması gerekmektedir.…”

“…Ancak demiryolu traversleri hakkında dünya genelinde yaygın kabul gören eğilme modülü veya kütle değerleri henüz yayımlanmamıştır. Hâlbuki birbirinden çok farklı elastisite modülü ve kütleye sahip mevcut traverslerin davranışları ve üzerlerine gelen yükler birbirlerinden çok farklı olmaktadır [41]. Bu durum, mevcut test ve dizayn yöntemlerinin yetersizliğini gözler önüne sermekte ve demiryolu kuruluşları açısından büyük endişe ve kararsızlığa neden olmaktadır [41,44,45].…”

A DEM study on the effects of sleeper elasticity on vertical railway track settlement

“…The interaction between the central components meaning rails, sleepers, and the ballast bed in dynamic load cases is particularly interesting. Literature has shown that the sleeper's mechanical properties strongly influence the total stiffness of the track and its long-term settlement behaviour and has more impact than the support modulus of the ballast bed [1,2,3]. In laboratory tests it was shown that under static loading soft sleepers develop a pronounced W-shaped deflection profile along their length and apply less uniformly distributed pressure onto the ballast bed with pressure peaks directly below the rails [2,3,4].…”

“…Literature has shown that the sleeper's mechanical properties strongly influence the total stiffness of the track and its long-term settlement behaviour and has more impact than the support modulus of the ballast bed [1,2,3]. In laboratory tests it was shown that under static loading soft sleepers develop a pronounced W-shaped deflection profile along their length and apply less uniformly distributed pressure onto the ballast bed with pressure peaks directly below the rails [2,3,4]. However, in long-term experiments with numerous load cycles a hogging shape of the sleeper was observed because the resilient movement of the sleeper ends lead to substantial gapping in that region, which can accelerate ballast deterioration due to impact loads and thus sleeper settlement [4,5].…”