Curious Civil Engineer

Types of Welding There are different types of welding used in steel structures, one of the most common being arc welding . In arc welding, the process uses a welding rod (electrode) to generate heat through an electric arc. The heat melts both the base metal and the tip of the electrode, allowing molten droplets of the electrode to deposit and fuse with the base metal. During this process, the weld area must be protected from atmospheric contamination. This protection is provided by inert gas or a vapor shield produced from the burning of the electrode coating. If this protective gas shield is not present, oxygen and nitrogen from the air may enter the molten weld metal, resulting in porosity , reduced toughness, and a brittle weld . Electrodes used in arc welding are classified into two types: Heavily-coated electrodes : Commonly used for structural welding, as they provide adequate shielding to protect the molten weld pool. Lightly-coated electrodes : Provide minimal shieldi...

A pressure reducing valve (PRV) , also known as a pressure breaking valve , is used to reduce and regulate fluid pressure to a specific, safe value in order to protect downstream equipment and piping systems. These valves are commonly used in water supply and hydraulic systems , where the inlet pressure may be higher than the pressure rating of the downstream components. In such cases, the pressure reducing valve ensures that the downstream pressure remains within the allowable range of the equipment and pipes, preventing possible damage or system failure. The figure below shows the main components of a pressure reducing valve, which typically include a diaphragm , spring , inlet , and outlet . The valve is set to a preset pressure value . When the inlet pressure exceeds this preset limit, the diaphragm is pushed upward, compressing the spring and closing the valve partially to restrict flow — thereby reducing the downstream pressure. Conversely, when the inlet pressure drops bel...

Flexible pavement is composed of several layers that work together to distribute traffic loads to the subgrade. These layers are generally divided into aggregate layers and asphaltic layers , each serving a specific function to ensure strength, stability, and durability of the pavement. Aggregate Layers The aggregate portion of the pavement usually consists of the subbase , roadbase , and sometimes a wet mix macadam (WMM) layer. These layers play a crucial role in supporting the asphaltic layers above and ensuring that loads are transferred smoothly to the subgrade without excessive settlement or deformation. 1-Subbase The subbase is a mixture of fine and coarse aggregates placed directly above the existing subgrade. Its main purpose is to improve the pavement’s overall bearing capacity, minimize settlement, and provide a uniform surface for the upper layers. Typically, the subbase should have a California Bearing Ratio (CBR) of not less than 30. The minimum thickness is usually abo...

Micropiles , also known as mini piles , are small-diameter piles typically up to 300 mm in diameter. They are used in situations where conventional piling methods are not feasible — such as in areas with restricted overhead clearance or where there is a need to minimize disturbance to nearby structures . Micropiles are constructed by drilling a borehole , installing reinforcement (usually a steel bar or cage) , and then grouting the hole. Despite their small diameter, micropiles can resist considerable axial loads while carrying minimal lateral loads . The axial load is primarily resisted by the steel reinforcement , which transfers the load to the surrounding soil through skin friction . Due to their small cross-sectional area, end-bearing resistance is generally neglected in micropile design. Types and Design Principles Micropiles can be designed to serve two main purposes: Direct Load Transfer (Structural Micropiles) In this common application, micropiles are designed to...

Reinforcement splicing or overlapping is a fundamental requirement in reinforced concrete structures. Because reinforcement bars (rebars) are manufactured in limited standard lengths—typically 12 m —it becomes necessary to splice or overlap them to achieve the required continuity in structural members. The main purpose of a splice is to ensure smooth stress transfer between adjacent bars through the surrounding concrete. The overlap length, commonly known as the splice length , must be long enough to safely transfer the tensile stresses from steel to concrete without causing bond failure. It is recommended to avoid splicing in high-stress zones such as areas of maximum moment, and to stagger the splices to prevent congestion and reduce stress concentration. The ACI 318-19 providing the following recommendatin and requirement for the lap splicing: 1. Splice Limitation by Bar Size Lap splicing is not permitted for reinforcement bars larger than 36 mm in diameter. 2. Non-Contact L...