Arif Ulu

Polymer-based materials have become increasingly used in concrete production and various engineering applications due to their versatile properties. In particular, polymer concrete (PC) has become a preferred reinforcement material in the construction industry. Various studies have been carried out to evaluate the performance of PC and to improve its mechanical properties by adding different admixtures. This study investigates the effects of fine materials such as iron powder (IP) and blast furnace slag (BFS) on the mechanical performance of PC. Within the scope of the study, samples with 5% and 10% IP, 5% and 10% BFS, 2.5% IP + 2.5% BFS and 5% IP + 5% BFS were prepared. These specimens were cured in the same laboratory environment and subjected to mechanical tests at the end of the 7th day. The results of the mechanical tests were compared to reveal the effect of fine materials on the performance of the PC. The potential of an artificial neural network (ANN) model is investigated to replicate real-world outcomes. The findings provide valuable insights into the potential of iron powder and blast furnace slag as admixtures to improve the mechanical properties of PC.

In the construction and infrastructure sector, efforts are being made to find faster and more efficient materials. Polymer concrete (PC) challenges traditional concrete with its fast setting, durability and abrasion resistance. While studies on PC strength are abundant in the literature, studies on the effects of resin amount on damping capacity are fewer than mechanical performance. In this paper, the effect of resin proportion on damping capacity is investigated by modal tests. PC mixtures in the production with different resin proportions (11‒19%) were poured into molds of 10x25x500 mm, using aggregates of up to 3.15 mm in size. After 14 days, the natural frequency and damping ratios of the specimens up to 1000 Hz were determined in modal tests. While the damping ratio (DR) decreased in resin contents up to 17%, the results of the specimens with 19% resin ratio increased. However, when the products with the same resin ratio are analyzed, the random distribution of the aggregate affects the damping capacity. The main reason of negative correlation between resin amount and DR is the filler amount in the mixture. Because of the production consistency, fluidization of all the mixtures is prevented by adding fillers. Therefore, the impact of the resin amount on DR is limited or even negative. Besides that, to compare measurement results finite element method (FEM) analyzes are conducted. It can be said that the natural frequencies are not suited well especially in high frequency ranges due to frequency dependent properties (visco-elastic) of PC.

This study aims to determine the stiffness values of under sleeper pad (USP) and rail pad (RP) components to reduce the high-amplitude vibrations that occur in the transition zones of some specific structures such as viaducts in ballasted railways. The conventional method of simulating USPs and RPs as spring–dashpot elements in the Kelvin–Voigt model is inadequate due to the absence of frequency and temperature dependencies in the model. The study proposes a new analytical model that considers USPs and RPs as viscoelastic (VE) materials and integrates them into the ballasted railway superstructure model by adding unit masses avoiding mathematical singularity. The process includes material testing, field measurements, and validation of the proposed model with finite element model analysis. The effect of ambient temperature and material modelling on the superstructure’s dynamic response in the frequency domain is analysed in detail. To account for VE behaviours of the resilient elements, the generalised Maxwell model (GMM) is chosen via unit mass implementation compared to other VE models. The obtained results show that the dynamic response of the railway superstructure is 8–10 times sensitive to temperature variation. This demonstrates how important it is to include the temperature-dependent dynamics of the elastomer material in the model. According to the other results that were obtained, the use of USP in transition zones does not solve the vibration problem radically. Bridge dynamic responses are also sensitive to the mass of the bridge rather than its stiffness.

Demiryoluna bağlı titreşimler, yolcuların veya demiryolunun çevresinde yaşayan insanlar için bastırılması gereken en önemli sorunlardan biridir. Titreşimlerin öncelikle kaynakta, yani demiryolu üzerinde bastırılmaya çalışılması esastır. Bu nedenle, demiryolu üst yapı bileşenleri, titreşim yalıtımında kullanılan ray pedleri gibi çeşitli elastik elemanlar içerir. Bu çalışmada, İstanbul demiryolu trafiğinde kullanılan iki farklı demiryolu üst yapısı, demiryolu aracı çeşitli hızlarda geçerken test edildi ve tekerlek-ray etkileşiminin oluşturduğu titreşimler, yolcu konforu ve çevre ile ilgili standartlara uygun olarak karşılaştırıldı. Yayılan titreşimleri karşılaştırmak için aynı hat üzerinde yerleştirilmiş tek ve çift elastomerik tabakalara sahip demiryolu üstyapıları kullanılmıştır. Standartlara göre bazı değerlendirmeler içeren bu deneysel kıyaslama çalışmasında, bu iki demiryolu üst yapı tipinin hafif metro hatlarında titreşim yalıtımı açısından davranışları ölçüm sonuçları kullanılarak ortaya konmuştur. Sonuç olarak, üstyapıda tek katman yerine çift katmanlı elastomer kullanıldığında, hat çevresinde yaşayan insanların konfor seviyelerinde %64’e, araç içerisinde bulunan yolcuların konfor seviyelerinde ise %54 varan iyileşme gerçekleşmiştir. Ayrıca, hat çevresinde bulunan binaların güvenliği bakımından yapılan araştırmada 70 HZ’den büyük titreşimlerde anlamlı bir azalma gözlenmiş ve hatta en az 5 m mesafeye kadar konut amaçlı bina yapılabileceği sonucuna ulaşılmıştır.

Purpose: In this study, a railway superstructure is modeled with a new approach called locally continuous supporting, and its behavior under the effect of moving load is analyzed by using analytical and numerical techniques. The purpose of the study is to demonstrate the success of the new modeling technique. Design/methodology/approach: In the railway superstructure, the support zones are not modeled with discrete spring-damping elements. Instead of this, it is considered to be a continuous viscoelastic structure in the local areas. To model this approach, the governing partial differential equations are derived by Hamilton’s principle and spatially discretized by the Galerkin’s method, and the time integration of the resulting ordinary differential equation system is carried out by the Newmark–Beta method. Findings: Both the proposed model and the solution technique are verified against conventional one-dimensional and three-dimensional finite element models for a specific case, and a very good agreement between the results is observed. The effects of geometric, structural, and loading parameters such as rail-pad length, rail-pad stiffness, rail-pad damping ratio, the gap between rail pads and vehicle speed on the dynamic response of railway superstructure are investigated in detail. Originality/value: There are mainly two approaches to the modeling of rail pads. The first approach considers them as a single spring-damper connected in parallel located at the centroid of the rail pad. The second one divides the rail pad into several parts, with each of part represented by an equivalent spring-damper system. To obtain realistic results with minimum CPU time for the dynamic response of railway superstructure, the rail pads are modeled as continuous linearly viscoelastic local supports. The mechanical model of viscoelastic material is considered as a spring and damper connected in parallel.