The President of the Engineering Institute clarified why 36 ten-wheel trucks weighing a total of over 900 tons were used to test shear strength and load capacity of bridge beams before opening the M82 Expressway, noting that the structure's piles are driven deep into the hard soil layer for a lifespan exceeding 70 years.
The Department of Highways and the Engineering Institute of Thailand inspected the structural strength of the M82 Expressway to meet standards ahead of its planned opening at the end of August.
The Ministry of Transport and the Department of Highways plan to open the new M82 motorway section from Bang Khun Thian to Ban Phaeo for public trial use starting 28 August 2026, accommodating cars, trucks, and buses with speed limits between 65-80 km/h.
Before opening, 36 heavy trucks were placed on the new M82 motorway bridge to test the construction's strength, with a combined weight exceeding 900 tons. Engineering considerations explain why exactly 36 ten-wheel trucks were used.
Thairath Online's special news team interviewed Associate Professor Anek Siripanichkul, President of the Engineering Institute of Thailand under Royal Patronage (EIT), about the use of 36 ten-wheel trucks on the motorway. The test targeted the bridge beam that collapsed on 15 January in the construction area of Highway No. 82 (M82 motorway) section from km 29+772 to km 31+207 on Rama 2 Road. The reason for using 36 ten-wheel trucks was to test the durability of the bridge piers, with each truck weighing 25 tons, totaling 900 tons.
During construction of contract 1 (km 11+959 to km 14+535), a similar collapse occurred; that test involved a 600-ton load. Failure to thoroughly verify structural integrity before public use would pose serious danger. This time, the test used a 900-ton load, moving trucks to assess shear, bending, distortion, and deflection of the bridge beams. The load reflects the Department of Highways' standard of 25-ton ten-wheel trucks.
Associate Professor Anek explained that before entering the motorway, a weigh station is installed, crucial for preventing overweight vehicles from accessing the bridge. This uses a 'Weight in Motion' system that measures the load of vehicles as they pass. Controlling vehicle weight on the bridge is essential. In designing bridges here, the use of 25-ton ten-wheel trucks, which are heavier than international standard trucks, meets good standards. The measured deflection was minimal, about 5-6 millimeters, whereas the maximum allowable deflection for bridge beams is approximately 37 millimeters.
Associate Professor Anek revealed that the Engineering Institute was invited by the Department of Highways to participate in a Road Safety Audit, assessing road safety. Sensors installed on the piers measure forces to ensure they do not exceed material limits. The audit also examines lighting and lane markings, though wire theft often causes power outages. Therefore, reflective guiding plates are used so traffic lanes remain visible even during blackouts or rain, enforcing a speed limit of 80 km/h. After the trial period, tolls will be collected starting two years from the opening date.
Associate Professor Anek further explained that the bridge piles are driven deep into the hard soil layer, so the foundation and bridge columns barely move, sink, or settle. Most settlement occurs during construction of fixed load structures and then stops. The bridge's fixed load capacity is quite high compared to the vehicle weights used in testing. He emphasized that the Department of Highways should regularly inspect and maintain the bridge, including joints and expansion gaps, which may change size or become uneven and require upkeep. Generally, a structure designed at this level has a minimum service life of about 70 years.
