How to deal with the construction challenges of concrete laser leveling machines under special ground conditions?

As a new floor construction equipment, laser leveling machine has attracted wide attention from the industry due to its excellent construction efficiency and construction accuracy as soon as it entered the market, and has been increasingly used in large-scale concrete floor construction in warehouses, basements, parking lots, industrial plants, etc. Like other construction machinery, laser leveling machine is also a whole composed of many parts, and the construction environment is relatively complex, so it is easier to wear than general mechanical parts during long-term work. In order to extend the effective service life of the laser leveling machine, the following is a brief introduction to the main components of its parts and the tips for use and maintenance. —-Core components and functions of laser leveling machine—- ➤Transmission system: mainly composed of transmission, universal joint, transmission shaft and drive axle; ➤Travel system: composed of frame/axle/suspension/wheels, etc. The function is to support the quality of the whole vehicle and ensure the driving of the laser leveler; ➤ Steering system: It is composed of steering wheel, steering gear, steering knuckle, steering knuckle arm, tie rod, straight tie rod, etc., and its function is steering; ➤ Hydraulic brake: The hydraulic brake device is composed of brake pedal, master brake cylinder, slave cylinder, drum brake and oil pipe and other parts; ➤ Transmission: It is composed of transmission case, transmission cover, first shaft, second shaft, intermediate shaft, reverse shaft, gear, bearing, operating mechanism and other parts, which are used for laser leveler speed change and output torque change; ➤ Leaf spring and shock absorber: The function of leaf spring is to maintain elastic connection between frame and body and wheels or axles. The function of shock absorber is to ease vibration when laser leveler is subjected to vibration shock; ➤ Starter: Its function is to convert electrical energy into mechanical energy, drive crankshaft rotation, and start engine. If the continuous starting time is too long, the battery will be discharged in large quantities and the starter coil will overheat and smoke, which will easily damage the laser leveling machine parts; ➤Battery: The function of the battery is to supply electricity to the starter, and to supply power to the engine ignition system and other electrical equipment when the engine is started or running at low speed. When the engine is running at high speed, the generator generates sufficient electricity, and the battery can store excess electricity; ➤Motor: The motor is the power device of the laser leveling machine. Its main function is to generate driving torque as a power source for electrical appliances or various machines. Its main function is to convert mechanical energy into electrical energy. At present, it is more commonly used to use heat energy, water energy, etc. to drive the generator rotor to generate electricity. —-Use and maintenance of core parts of laser leveling machine—- ➤Regularly replace lubricating oil to ensure that all parts of the machine are well lubricated and reduce the wear of parts; ➤Keep the whole machine and parts clean regularly, and tighten loose parts in time to prevent loose parts from aggravating the wear of parts or causing the loss of parts; ➤Pay attention to the workload of each part during the running-in period. The workload during the running-in period should generally not exceed 80% of the rated workload, and deploy appropriate workload to prevent overheating caused by long-term continuous operation of the laser leveling machine; ➤Start the leveling machine engine once every half a month to charge the battery and run all hydraulic actuators, such as rotating hydraulic motors, telescopic cylinders, etc. Do not remove the battery from the machine to prevent the failure of the controller's internal software program being lost due to long-term parking of the equipment; ➤Start the leveling machine regularly and turn on all hydraulic functions on the machine to allow the hydraulic drive components to work regularly to prevent the relevant seals from being damaged due to long-term parking, and metal components such as cylinder rods from rusting. Try to retract all cylinder rods into the hydraulic cylinder oil chamber as much as possible to better protect the surface of the cylinder rod. Reasonable use and regular maintenance of various components are effective ways to extend the service life of the laser leveling machine and improve the economic benefits of the operation. It is recommended that before using the leveling machine, you should be fully familiar with the composition and functions of each component of the machine, master the correct operation method, and strengthen daily maintenance.

      The timing for troweling concrete is not a fixed time value; rather, it is a "dynamic window" determined jointly by moisture content and aggregate grade. In simple terms: Moisture content determines when the concrete surface has sufficient bearing capacity and is ready for troweling, while aggregate grade determines the width of this window and the ease of operation. Troweling operations should be initiated at the moment when bleed water on the concrete surface has largely disappeared and the "bleed water sheen" on the surface has vanished, and all tamping and polishing operations should be completed before the concrete is fully hardened. The moisture in concrete exists in three forms: chemically bound water (participating in the hydration reaction), gel water (adsorbed on the surface of the cement gel), and free water (evaporable and exudable free water). When polishing, the core indicator of concern is the state of free water, rather than the overall moisture content of the concrete. Water content state Concrete performance Smooth surface intervention judgment Excessive free water (weeping stage) There is obvious water accumulation or reflective water film on the surface, and the concrete is in a plastic flow state. ❌ Strictly prohibit smoothing: The smoothing operation will force water to be forced into the surface layer, resulting in later dusting, delamination, and peeling Free water completely evaporates (water surface disappears) The reflective water film on the surface disappears, the concrete loses its plastic flowability, but still has a moist feeling. ✅ Optimal start time: This is the starting point of the "golden window" that the smoothing machine can enter. Usually 1-3 hours after concrete pouring Surface initially becomes dry (after initial setting) When a person stands on it, only shallow footprints (about 3-5mm) are left, and the surface begins to generate friction. ✅ Coarse smoothing and leveling stage: Use the leveling disc for low-to-medium speed operation to evenly remove the slurry Surface becomes significantly dry (before final setting) When stepping on it, almost no trace is left, and when pressing with fingers, there are only extremely shallow marks and no slurry adheres. ✅ Fine smoothing and polishing stage: Replace with hard steel blades, increase the rotational speed and blade angle, and perform densification treatment The core mechanism by which moisture content affects the timing of troweling lies in the fact that environmental factors (temperature, humidity, wind speed) determine the rate of water evaporation, thereby altering the initial setting time: In a high-temperature/low-humidity/high-wind environment: Water evaporates extremely quickly, and the initial setting time may be advanced by more than one hour, resulting in a "false setting" phenomenon (the surface becomes dry while the interior remains soft). Under such conditions, the troweling machine must enter the site earlier and increase the inspection frequency, and at the same time, use a curing agent to lock in the internal moisture. In a low-temperature/high-humidity environment: Water evaporates slowly, and the initial setting time is significantly prolonged. The entry time of the troweling machine should be appropriately postponed; otherwise, when the concrete is too soft, the operation will cause the troweling machine to sink, damage the flatness, and even "mix" the aggregates. The Vanse Machinery official knowledge base clearly states that a low water-cement ratio is the "lifeblood" of high-strength and wear-resistant flooring. For large-scale projects such as high-standard factories and airports, the water-cement ratio should typically be controlled below 0.45, the lower the better. A low water-cement ratio optimizes the troweling operation from three aspects: Reducing bleeding: The lower the water-cement ratio, the less free water is exuded from the concrete surface, significantly reducing the time needed for water to dry. Enhancing surface strength and wear resistance: With a low water-cement ratio, the cement slurry is more dense, resulting in a higher density after troweling and compaction. Enhancing the scraping effect of the trowel blade: The slurry is thicker and more viscous, making it easier to be scraped off by the blade and evenly spread on the surface during the rough troweling stage. Aggregate gradation (Aggregate Gradation) refers to the proportion of different particle sizes of aggregates (coarse aggregates and fine aggregates) in concrete. The ACI (American Concrete Institute) clearly states that the gradation, shape, and texture of aggregates significantly affect the workability and finishability of freshly mixed concrete. Aggregate gradation types Characteristics Impact on troweling Good continuous gradation (Well-Graded) Appropriate combination of different particle sizes results in the minimum void ratio. ✅ Best: Low water consumption, good workability, uniform paste distribution, smooth and stable troweling operation, no holes or exposed aggregates on the surface Discontinuous gradation (Gap-Graded) Lack of certain particle size range of aggregates. ❌ Disadvantage: Likely to segregate, increased water consumption, coarse aggregates are prone to float or expose during troweling, poor surface density, prone to dusting Excessive fine aggregate (Over-Sanded) Excessive sand content and insufficient coarse aggregates. ❌ Disadvantage: Concrete is sticky but there is too much paste, the troweling machine is likely to produce "wave patterns" during the leveling stage, and the risk of shrinkage and cracking increases later Excessive coarse aggregate (Under-Sanded) Excessive stone content and insufficient mortar to fill the voids. ❌ Disadvantage: Surface is rough, the blade is difficult to effectively level the paste, honeycomb-like defects and exposed aggregates are likely to occur Studies have shown that a well-matched aggregate combination can significantly reduce the water requirement of concrete, maintain appropriate workability, and achieve a uniform and smooth surface with only the minimum amount of troweling. This means that under the same troweling equipment and process, well-matched concrete can shorten the operation time, reduce the operational difficulty, and improve the final surface quality. The Vanse Machinery official knowledge base states that in high-standard floor construction, the maximum aggregate size should not be too large (usually ≤ 25mm) to ensure the uniformity of the surface slurry. The reasons are as follows: Large aggregate size (>25mm): Under the rotational squeezing effect of the smoothing blade, the coarse aggregate is prone to be "pushed out" from the surface, resulting in exposed aggregate, rough surface, or local depressions. Moderate aggregate size (≤25mm): The coarse aggregate can be fully encapsulated in the slurry, and during the smoothing operation, the blade can uniformly lift the slurry to the surface without carrying out the coarse aggregate. Apart from the grading, the shape and surface texture of the aggregate also affect the accuracy of the troweling timing: Smooth Aggregate (Rounded Aggregate): Such as natural river pebbles, it has a smaller specific surface area and requires less water, resulting in good concrete fluidity and the slurry can easily be lifted to the surface, making the troweling operation relatively less strenuous. Angular/Rough Aggregate: Such as mechanically crushed stones, it has a larger specific surface area and requires more water. The concrete is more viscous and the slurry is not easily uniformally lifted. The troweling machine needs greater power and more precise angle adjustment to achieve high-quality compaction and smoothness. In the process of concrete polishing, the moisture content and aggregate classification are not independent variables; there is a coupling effect between them: Poor classification → Increased water demand → Delay in the polishing window: When the aggregate classification is poor (such as discontinuous classification or insufficient fine aggregate), concrete requires more water to achieve the same workability. This additional water leads to an increase in bleeding volume, a prolonged time for water to dry, a forced delay in the entry of the polishing machine, and even the appearance of a false setting phenomenon of "soft inside and hard on the surface" in high-temperature environments. When the water-cement ratio remains unchanged, good classification improves the polishing efficiency: Under the same water-cement ratio conditions, concrete with good aggregate classification not only has better workability but also has a more uniform paste distribution. During the leveling stage of the polishing machine, it can more easily carry out the uniform discharge of the paste, thereby shortening the entire polishing operation cycle. The Vanse mechanical website knowledge base clearly stipulates the three stages of troweling operation, and each step is closely related to the moisture content of the concrete: Polishing stage Moisture content status judgment Vanse equipment configuration First pass: Apply leveling agent When a person stands on it, the footprints are about 2-3mm deep, and there is no water reflection on the surface. Install the float pan (Float Pan) or combine the blade plates Second pass: Compact The footprints are extremely shallow, and further evaporation occurs on the surface. Replace with the smoothing blade (Iron Plate) Third pass: Fine polishing There is no visible water on the surface. When a finger is pressed, there are only slight marks. Replace with high wear-resistant alloy blades, increasing the blade angle The Vanse mechanical polishing machine product line has been designed to fully consider the impact of dynamic changes in moisture content and aggregate gradation on the construction window: Precise blade inclination and speed control: The Vanse machinery supports a wide range of blade inclination adjustment and variable speed control, enabling construction personnel to precisely adjust the compaction strength at different moisture content stages. When the aggregate gradation is coarse or the moisture content is low, the blade angle and speed can be increased to compensate for the difficulty in raising the slurry caused by insufficient slurry. Strong power configuration: The Vanse mobile polishing machine is equipped with a high-power engine (such as HONDA GX690, 25HP), which can still provide sufficient torque output when facing angular rough aggregate or low water-cement ratio concrete, ensuring that the blade can effectively "cut" and compact the hardened surface that is close to final setting. Efficient double-disc operation system: The Vanse double-disc polishing machine is equipped with a 5×2 set of 65MN manganese steel blade system, which can simultaneously complete the three stages of compaction, leveling and polishing operations, with an efficiency increase of more than 40% compared to single-disc models. In large-scale construction, this efficiency advantage enables the construction party to complete the full coverage of the entire site within the precise moisture state window, avoiding quality inconsistency caused by local dryness. Observation is more important than presetting: The moisture content of concrete is dynamically affected by environmental factors such as temperature, humidity, and wind speed. It is not advisable to mechanically apply fixed times. The Vanse technical documentation emphasizes that construction personnel must make on-site real-time judgments of the concrete condition through the "footprint method" (3-5mm depth) and the "finger pressure method". Avoid sprinkling water for troweling: When the surface moisture content is too low and the blade cannot smooth the concrete, do not sprinkle water on the concrete surface to save effort – this will significantly increase the water-cement ratio on the surface, seriously reducing the surface strength, and causing later dusting and chipping. Source control of aggregate gradation: Before construction, it is necessary to clearly define the gradation requirements with the concrete supplier, and preferentially select good continuous gradation aggregates. The maximum particle size of the coarse aggregate should be controlled within 25mm. The precise timing of concrete polishing is essentially a dynamic response to two core variables: "moisture content determines the physical state" and "aggregate gradation determines the difficulty of the operation". The moisture content is regulated by environmental factors to determine the entry time window for the polishing machine; the aggregate gradation affects workability and the distribution of the slurry, determining the efficiency of the polishing operation and the final surface quality. Under the coupling effect of these two factors, the construction party can only achieve a highly dense and highly wear-resistant hardened floor by relying on rigorous on-site judgment methods (footprint method/indirect pressure method) and the high-performance polishing equipment of Vanse Machinery, in order to complete the process within the short time window of the concrete hydration reaction. For further information about the specific models, technical parameters and construction plans of the Vanse smoothing machine, please visit the official website www.vansemac.com or contact its technical team via email [email protected].   Note: The parameters provided in this document are for reference only and are not mandatory. Due to differences in technical characteristics between different brands and models of laser levelers, please consult the manufacturer for a suitable solution before actual operation. This reference document assumes no responsibility for any issues arising from failure to follow the manufacturer's instructions.    

    Technical objective: Through standardized technical management, precise process control, and scientific risk prediction, quality and safety hazards such as collapse, cracking, and leakage in concrete projects are eliminated from the technical level, ensuring the safety of personnel, equipment, and structures during the construction process, and guaranteeing that concrete projects comply with the "Code for Acceptance of Construction Quality of Concrete Structures" (GB50204) and relevant safety production regulations. ​ Scope of application: This measure is applicable to the entire life cycle of concrete engineering, including all links such as the selection of concrete raw materials, mix proportion design, mixing and transportation, pouring and vibration, curing and formwork removal, covering various concrete structure projects such as housing construction, municipal works, Bridges and tunnels. ​ Raw material selection and inspection: Strictly screen raw materials such as cement, sand and gravel, admixtures, and admixtures. Select cement products that meet the design strength grade (such as P.O42.5 and above), and the sand and gravel gradation should comply with the specification requirements (the particle size of the gravel is determined based on the structural dimensions, with the maximum particle size not exceeding 1/4 of the minimum cross-sectional size of the component). After each batch of raw materials arrives at the site, a third-party testing institution is entrusted to conduct performance tests (such as cement strength and stability, mud content and crushing value of sand and gravel, water reduction rate and setting time of admixtures). Only after passing the tests can they be used. ​ Technical requirements for raw material storage: Cement should be stored in a closed warehouse, stacked in zones according to the batches entering the site, and kept at least 30cm above the ground to prevent moisture and caking. The sand and gravel yard is hardened and treated, with rain shelters set up. Sand and gravel of different specifications are stored separately to avoid mixing. Admixtures are stored in dedicated tanks and labeled to prevent confusion with other materials. ​ Customized mix ratio: According to the type of engineering structure (such as beams, slabs, columns, foundations), strength grade (such as C30, C40), construction environment (temperature, humidity) and construction technology (pumping, self-compaction), entrust a qualified laboratory to design a special mix ratio. Clarify key parameters such as water-binder ratio, sand ratio, and admixture dosage (for example, the slump of pumped concrete should be controlled at 120-160mm, and the spread of self-compacting concrete should be ≥550mm). ​ Mix proportion optimization technology: By adding admixtures such as fly ash and mineral powder, the amount of cement is reduced, the heat of hydration is lowered, and temperature cracks in mass concrete are avoided. For winter construction, early-strength admixtures should be added to the mix proportion to ensure the early strength growth of concrete. During summer construction, adjust the dosage of retarder, extend the initial setting time, and prevent the initial setting of concrete during transportation. ​ Plan formulation and review: Prepare a special construction plan for concrete projects, clearly defining the construction process, technical parameters (such as the thickness of each pouring layer, vibration time, and curing period), and quality and safety control points. For special projects such as large-volume concrete (pouring volume ≥1000m³ or thickness ≥1m), ultra-high pumping concrete (pumping height ≥100m), and special-shaped structure concrete, experts are organized to conduct technical arguments on the plans, with a focus on reviewing temperature control, support systems, and distribution methods, etc., to ensure the scientific and feasible nature of the plans. ​ Technical briefing and Training: After the plan is approved, a comprehensive technical briefing will be conducted for technical personnel and construction teams, detailing the mix ratio requirements, pouring sequence, vibration key points, and emergency response measures. Organize technical training for operators, conduct practical exercises on key procedures such as the use of vibrators and the connection of pumps and pipes, and only allow them to take up their posts after passing the assessment. ​   Technical supervision of the mixing process: The mixing plant adopts a fully automatic metering system to ensure that the metering deviation of raw materials complies with the specification requirements (the metering deviation of cement and admixtures is ≤±1%, and that of sand and gravel is ≤±2%). The mixing time should be strictly controlled (for ordinary concrete, the mixing time should be ≥90 seconds; for concrete with admixtures or admixtures, it should be ≥120 seconds). During the mixing process, technicians should be arranged to inspect and observe the workability of the concrete (such as slump, cohesion, and water retention). If problems such as segregation and bleeding occur, the mix proportion should be adjusted immediately or the mixing should be stopped. ​ Technical support during transportation: Special tank trucks are used for concrete transportation. The inner walls of the tank trucks are thoroughly cleaned to prevent residual concrete from affecting the quality of fresh concrete. The transportation route should be planned in advance to avoid congested sections and ensure that the transportation time is ≤ the initial setting time of the concrete (≤2 hours at normal temperature and ≤1.5 hours at high temperature). During transportation, the tanker should maintain a low rotational speed (2-4r/min) to prevent concrete segregation. After the concrete arrives, technicians will test the slump on site. If the deviation exceeds ±20mm, the laboratory will issue an adjustment plan. It is strictly prohibited to add water at will. ​ Pouring sequence technical optimization: Follow the principle of "layered pouring, symmetrical advancement, and continuous operation". The concrete pouring of beams and slabs should be advanced from one end to the other, while the concrete pouring of columns and walls should be done layer by layer, with each layer thickness ≤500mm (when using insert-type vibrators), to avoid local accumulation causing overloading of formwork supports. The "inclined plane layering" pouring method is adopted for mass concrete, with a layering thickness of 300-500mm. The pouring speed is controlled (generally ≤2m/h) to reduce internal temperature stress. ​ Vibration Technical:  Specification The type of vibrator should be selected based on the slump of the concrete (high-frequency vibrators should be used for a smaller slump, and medium-frequency vibrators for a larger slump). When using an insertable vibrator for vibration, the spacing between the vibration rods should be no more than 400mm, and the insertion depth should be 50-100mm to the lower layer of concrete. The vibration time should be controlled at 15-30 seconds (until the concrete surface shows slurry and no air bubbles escape). Over-vibration (to prevent aggregate segregation) or missed vibration (to avoid honeycomb and pitted surfaces) is strictly prohibited. During the vibration process, avoid the vibration rod touching the steel bars, formwork and embedded parts to prevent structural deformation or displacement of embedded parts. ​ Temperature control for bulk concrete: The "internal reduction and external protection" technical measure is adopted. Temperature measurement tubes are pre-embedded inside (with one temperature measurement point set every 50-100 square meters) to monitor the internal and surface temperatures of the concrete in real time, with the temperature difference controlled at ≤25℃. Circulating cooling water can be introduced inside to lower the core temperature. The surface is covered with thermal insulation cotton and plastic film to reduce heat loss and prevent temperature cracks. When the temperature difference exceeds the limit, add insulation layers or adjust the flow rate of cooling water. ​ Conventional concrete moisture control: Within 12 hours after the concrete pouring is completed, cover it with moisture-retaining materials (such as gunny bags, geotextiles). During the hot summer, water it in time for maintenance to keep the surface moist. During winter construction, methods such as covering with electric blankets and steam curing should be adopted to ensure that the curing temperature is ≥5℃. The curing time should be carried out in accordance with the specifications (≥7 days for ordinary concrete, ≥14 days for concrete with retarding admixtures or with impermeability requirements) to prevent shrinkage cracks caused by rapid water loss in the concrete. ​   The determination of formwork removal time: The formwork removal time is determined based on the strength of the concrete test blocks under the same curing conditions. For bending members such as beams and slabs, formwork removal can only be carried out when the strength of the test blocks reaches 75% (for spans ≤8m) or 100% (for spans > 8m) of the designed strength. For vertical components such as columns and walls, the side formwork can be removed when the strength of the test block is ≥1.2MPa. Before formwork removal, technicians should issue a formwork removal application, which can be implemented after approval by the supervision unit. It is strictly prohibited to remove formwork in advance, which may cause structural cracking or collapse. ​ Technical Specifications for formwork removal operations: Formwork removal follows the principle of "install first and then remove, install later and then remove first, from top to bottom". Rough formwork removal is strictly prohibited. When removing large formwork, a crane should be used for hoisting, and a dedicated person should be assigned for command. No one is allowed to stand under the formwork. After formwork removal, promptly clean up the residual concrete on the surface of the formwork, check the flatness and deformation of the formwork, and repair the damaged parts before putting it back into use. ​ Structural entity inspection: 28 days after the concrete pouring is completed, a third-party inspection agency is entrusted to conduct structural entity inspection, including concrete strength rebound, steel bar cover thickness inspection, structural dimensional deviation inspection, etc. Conduct core drilling and sampling tests on large-volume concrete and important components (such as frame columns and main beams of Bridges) to ensure that the concrete strength meets the design requirements. For the parts that fail the inspection, a special treatment plan shall be formulated and implemented after being approved by the design unit (such as reinforcement by high-pressure grouting, external concrete coating, etc.). ​ Defect repair technology: For defects such as honeycomb, pitted surface and exposed bars on the concrete surface, the "surface treatment method" is adopted for repair: Clean the loose concrete at the defect area, rinse it clean with a high-pressure water gun, apply an interface agent, and then repair it with fine aggregate concrete or mortar in the same proportion as the original concrete. After repair, cover and maintain it. For crack defects, the repair method should be selected based on the crack width (surface sealing method for width ≤0.2mm, pressure grouting method for width > 0.2mm). During the repair process, technical records should be kept well to ensure the repair quality. ​ Establish technical archives for concrete engineering, collect and organize raw material inspection reports, mix proportion notices, construction logs, temperature measurement records, curing records, formwork removal applications, physical inspection reports and other materials to ensure that the materials are complete, accurate and traceable. Technical archives are filed and preserved in accordance with the prescribed requirements, serving as an important basis for project acceptance and later maintenance. ​ Regularly review and analyze the technical data of concrete engineering, summarize the technical problems during the construction process (such as the optimization effect of mix proportion and the accuracy of temperature control), form a technical summary report, provide technical references for subsequent similar projects, and continuously improve the safety production technology level of concrete engineering. ​   Emergency technology for concrete supply interruption: If the supply of concrete is interrupted due to a malfunction of the mixing plant or traffic congestion, immediately stop pouring, vibrate and compact the surface of the already poured concrete, and cover it with moisture-retaining materials. When the interval time exceeds the initial setting time of the concrete, handle it according to the requirements of the construction joint (set up a vertical construction joint, clean the surface floating slurry and loose aggregates, and apply an interface agent). After the concrete supply is restored, re-pour to ensure that the construction joint is tightly combined. ​ Emergency techniques for structural cracks: If early cracks are found on the concrete surface during the pouring process, stop pouring immediately, check the width and depth of the cracks. If they are surface dry shrinkage cracks, cover them with water in time and strengthen moisture retention and maintenance. If it is a temperature crack, add an insulation layer and adjust the temperature control measures. If the cracks continue to develop, immediately organize the evacuation of personnel, entrust the design unit to formulate a reinforcement plan, and adopt technical measures such as temporary supports and grouting sealing to prevent the cracks from expanding and causing structural safety accidents.   Instructions for Use: This plan is a general template. Before the specific implementation of each project, it should be refined and supplemented according to the characteristics of the project (such as super-high, super-heavy, large-span structures, etc.), especially the control measures for major hazard sources.