Simulating the Time-Cost Trade-Off of Construction Projects: A Case Study of a Mall–Expansion Building Project

Abstract

Efficient project scheduling is essential in modern construction, where time and cost are interdependent. Time-Cost Trade-Off (TCTO) analysis remains a major challenge, particularly in urban commercial projects where delays and cost overruns can significantly affect investment returns. The Mall-Expansion project in Semarang, designed to accommodate increasing visitors and improve public function, is currently delayed by 10.49% from its March 2025 target, mainly due to technical and weather-related issues. This study investigates acceleration strategies for a 10-storey parking and retail building using TCTO simulation. Data were collected from project documentation, field observations, and interviews with the contractor. Seven options were analysed, focusing on increasing labour, overtime, and deploying heavy equipment for critical path structural activities. The results indicate that additional labour was the most effective and efficient acceleration strategy, reducing the project duration by 42 days (8.11%) with an increased direct cost of IDR 612,406,406.65 (2.08%). However, the shortened duration reduced indirect costs, leading to a relatively small net increase in total project cost. When compared with the projected delay penalty of IDR 3,231,640,625.79, this strategy provides a relative cost advantage of 18.95% by minimizing potential delay losses. In contrast, overtime is less optimal in terms of cost and productivity, while heavy equipment addition is constrained by site limitations. The simulation showed strong validity, with a deviation of less than 0.01%. The findings confirm that increasing labour provides the best balance between time savings and cost control, highlighting the value of data-driven decision-making in optimising project performance under real construction conditions.