en Railway Transportation Railway Transportation پژوهشي Research <div style="text-align: justify;"><span style="font-size:10.0pt"><span style="line-height:115%"><span new="" roman="" style="font-family:" times="">The phenomenon of unsupported sleepers is considered one of the most critical factors affecting the dynamic performance of ballasted railway tracks. Disrupting the contact between the sleeper and the ballast leads to increased deflection, stress concentration, and reduced track stability. This study aims to numerically analyze and simulate the dynamic effects of unsupported sleepers, focusing on their numbers and layout patterns in the ballasted railway tracks. For this purpose, a three-layer mechanical model consisting of rail, sleeper, and ballast was developed in MATLAB, and its results were compared with an equivalent finite element model created in ABAQUS. The MATLAB model employs mass, stiffness, and damping matrices along with a time-dependent moving load to evaluate the system&#39;s response under various unsupported sleeper conditions. In the ABAQUS model, sleepers and ballast were modeled as concentrated masses, with their interactions represented via equivalent spring-damper systems; loading was applied incrementally along the train path. The results indicate that increasing the number of unsupported sleepers&mdash;particularly in sequential arrangements&mdash;significantly amplifies rail deflection and mid-span stress, with the most critical response observed in the case of three-consecutive-unsupported-sleepers. These findings indicate the necessity of continuous monitoring and preventive maintenance of unsupported zones to ensure track safety and extend structural service life.</span></span></span></div> Unsupported sleeper , Ballasted railway track , Dynamic analysis , Rail deflection ,Sleeper displacement , Ballast settlement 34 48 http://ijrare.iust.ac.ir/browse.php?a_code=A-10-250-3&slc_lang=en&sid=1 Alireza Bani Asadi 180031947532846002959 180031947532846002959 No Msc student, School of Railway Engineering, Iran University of Science and Technology, Tehran, Iran. Mohammad Bordbar 180031947532846002960 180031947532846002960 No Msc student, School of Railway Engineering, Iran University of Science and Technology, Tehran, Iran. Seyed Ali Mosayebi 180031947532846002961 180031947532846002961 Yes Assistant Professor, School of Railway Engineering, Iran University of Science and Technology, Tehran, Iran. Jabbar Ali Zakeri 180031947532846002962 180031947532846002962 No Professor, School of Railway Engineering, Iran University of Science and Technology, Tehran, Iran