Civil Engineering Design: Buildings, Bridges Drainage · Forensic · Construction Supervision

Full-service civil engineering design — SPN Soil Engineering

SPN Soil Engineering provides civil engineering design by COE-licensed engineers, grouped as: new structural design (RC, steel, bridges, industrial floors, machine foundations, solar mounting structures); assessment and extension of existing structures; drainage, roads and utilities; and forensic engineering, temporary works and construction management. Structures are analyzed by FEM with ANSYS and SAP2000. Every drawing set is certified by a licensed engineer and can be used for building-permit submissions and other relevant agencies. Safe structural design starts with accurate soil data — SPN provides soil investigation and full-service geotechnical engineering design within the same team.

If you already have drawings or an existing structure and only need checking and signing, SPN offers certification of drawings, calculation reports and engineer's certificates by a Senior Professional Civil Engineer, covering certification of drawings for permit submissions and structural safety certificates for existing buildings for extensions, machinery installation, solar panels or property sale and purchase.

1. Structural design of buildings, bridges and industrial works (Structural Design)

Design of reinforced concrete and structural steel to international standards, including specialized factory and solar farm structures, with FEM analysis for complex work.

• RC Structure Design — reinforced concrete (ACI 318, EIT standards)Design of all types of reinforced concrete structures: columns, beams, slabs, shear walls and footings to ACI 318 and EIT standards. Forces are calculated with the load combination 1.4DL + 1.7LL (Ministerial Regulation on structural design of buildings, B.E. 2566 (2023)) or 1.2DL + 1.6LL (ACI 318-19), depending on the standard used for the project, for work of every size from houses to multi-story high-rise buildings.
• Steel Structure Design — structural steel (AISC 360 LRFD/ASD)Design of structural steel for factories, warehouses, portal frame buildings and special structures. Wind load is analyzed to DPT 1311-50 or ASCE 7, every connection (bolted, welded) is designed, and critical connections are checked by FEM in ANSYS.
• Bridge and Culvert Design — bridges and culverts (AASHTO LRFD)Design of T-beam and box girder bridges, steel bridges, box culverts, pipe culverts and wing walls to AASHTO LRFD and Department of Highways standards, with HL-93 live load, seismic load and scour protection for bridge foundations.
• Industrial Floor Design — factory and warehouse slabs-on-ground (ACI PRC-360, TR34)Design of concrete slabs-on-ground for factories and warehouses to carry point loads from rack posts, forklift wheels and distributed loads from stored goods, following ACI PRC-360 and TR34. We set thickness, reinforcement or fiber, joint layout and sub-base, using the modulus of subgrade reaction (k) from a Plate Bearing Test together with soil investigation data.
• Machine Foundation Design — foundations for vibrating machinery (ACI PRC-351.3)Design of foundations for rotating and impact machinery such as pumps, compressors, generators and heavy machinery, following ACI PRC-351.3. The natural frequency of the foundation-soil system is checked to stay away from the operating frequency (resonance), and vibration amplitude is kept within the manufacturer's limits, using soil parameters from actual site investigation.
• Solar Mounting Structure — rooftop and ground-mount solar structuresCapacity check of existing roof framing and purlins before installing rooftop solar panels, and design of ground-mount panel structures for wind load to DPT 1311-50 or ASCE 7, including uplift and lateral forces transferred to the piles. Pile capacity is confirmed by Lateral Load Test and Tension Load Test on solar farm projects.

2. Assessment, extension and strengthening of existing structures (Existing Structures)

For buildings, floors, roads, bridges and piers already in service — we calculate whether they can take new loads, where strengthening is needed, and design extensions that work safely with the existing structure.

• Load Rating / Capacity Assessment — load capacity of existing structures (ACI 562, AASHTO MBE)Calculation of the actual load capacity of structures in service, such as building floors that will take new racks or machinery, concrete roads and yards for cranes or heavy trucks, bridges and piers. We use the original drawings together with actual measurements (GPR rebar scanning and Core Test), following ACI 562 for existing concrete structures and the AASHTO Manual for Bridge Evaluation (MBE) for bridges. When needed, results are confirmed by a Floor Load Test or bridge load test.
• Extension and Change of Use — design for extensions, alterations and change of building useWe inspect the existing structure and calculate the added loads from extra floors, enlarged areas or a change of building use (e.g. house to office, warehouse to factory), then design the extension and the members that need strengthening, with a drawing set and calculation report for permit submission under the Building Control Act. For house extensions on soft soil, the extension structure is designed separately to reduce differential settlement (read what to check in an old building before extending it).
• Structural Retrofit and Strengthening — strengthening existing structuresThe remaining capacity of the existing structure is analyzed by FEM, and strengthening is designed using Carbon Fiber Reinforced Polymer (CFRP) following ACI 440.2R, steel jacketing, concrete jacketing or added shear walls, for added floors, change of use and seismic upgrades.
• Damage Assessment Report — post-event damage assessmentAssessment of structural damage after floods, earthquakes and liquefaction risk, fires or accidents. Damage is classified (Minor, Moderate, Severe, Irreparable) with recommendations to repair, strengthen or demolish (read post-earthquake building inspection).

3. Drainage, roads and utilities (Drainage, Road & Utility Design)

From project-level flood studies and stormwater, sewer and pavement design to underground utility structures, to the relevant standards.

• Flood Study — project-level flood and hydrology studies (HEC-HMS, HEC-RAS)Rainfall analysis with intensity-duration-frequency (IDF) curves, catchment flood flow calculation with HEC-HMS, and flood level modeling by return period with HEC-RAS, to set fill levels, ground-floor levels and detention measures so the project's drainage does not worsen impacts on neighboring areas. For industrial estates, solar farms, warehouses and projects that need environmental reports.
• Storm Drainage Design — storm drainage and stormwater managementPeak flow is calculated with the Rational Method (Q = CiA) or the SCS Curve Number for the specified return period. We design storm drains, open channels, catch basins and retention/detention ponds to reduce flooding on the project site.
• Sanitary System Design — sewer and sanitary systemsDesign of sewer systems, both gravity flow and pressure systems, and wastewater treatment based on BOD loading and Pollution Control Department standards, supporting EIA conditions and industrial factory standards.
• Road and Pavement Design — roads and concrete pavements (AASHTO)Design of pavement structures, both flexible (asphalt) and rigid (concrete), by AASHTO 93 or the Mechanistic-Empirical method, calculating subbase, base and surface layer thicknesses from traffic load (ESALs).
• Utility Structure Design — underground utility structuresDesign of structures for large pipes (pipe bedding, thrust blocks), utility tunnels, underground power cables and duct banks to ACI 318 and ASCE 7, calculating earth pressure, water pressure and traffic load above.

4. Forensic engineering, temporary works and construction management (Forensic, Temporary Works & Construction Management)

Investigating the cause of engineering damage, designing temporary structures during construction, preparing tender documents and managing projects so they follow the drawings and standards.

• Forensic Engineering InvestigationInvestigation and analysis of the true cause of damage to buildings, bridges, foundations and all types of construction. Technical evidence is gathered together with non-destructive structural testing (NDE), and an Expert Witness Report certified by a licensed engineer is prepared for insurance claims, contract disputes and legal proceedings. Homeowners who suspect a foundation problem can first read 5 warning signs of house foundation problems.
• Temporary Works Design (BS 5975)Design and checking of temporary structures during construction: formwork shoring and load-bearing scaffolding (falsework) following BS 5975, crane outrigger pads with bearing capacity checks of the soil under the outriggers, and reaction frames/kentledge for load testing. For temporary earth retaining in deep excavations, see geotechnical design.
• BOQ, TOR and Specification — quantity take-off, cost estimating and tender documentsQuantity take-off from construction drawings, bills of quantities and prices (BOQ), construction cost estimates, and terms of reference (TOR) and technical specifications for tendering on both public and private projects. Everything is prepared from the same drawing set and calculations, so it is traceable.
• Construction SupervisionSupervision of construction so it follows the drawings, specifications and engineering standards, with material testing, soil compaction (Field Density Test), concrete strength (Concrete Cylinder Test) and welding inspection, plus RFIs, site instructions and progress reports.
• Construction ManagementConstruction project management based on the triple constraint (scope, time, cost): master schedule with CPM/Primavera, cash flow and payment control, coordination of main contractors and subcontractors, and systematic handling of change orders and claims.

Civil engineering design services summary

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Durations are approximate ranges after complete data is received and depend on project size and complexity. For items marked "Per scope", the engineer will state the delivery date in the quotation.

Software and standards SPN uses for design

• ANSYS Mechanical / Workbench — FEM AnalysisStress, strain, deflection, fatigue and dynamic analysis for complex structures such as connection details, pressure vessels, and wind load simulation with CFD.
• SAP2000 / ETABS (CSI) — Building and Bridge Analysis2D and 3D analysis of buildings and bridges, supporting static, dynamic, seismic (response spectrum) and time history analysis to DPT 1301/1302-61 and ASCE 7 (read seismic building design to DPT 1301/1302-61).
• AutoCAD, Revit — Structural Drafting and BIMConstruction drawings and shop drawings in AutoCAD 2D/3D and Revit Structure for work that needs BIM integration, delivered as DWG, DXF, PDF and IFC files.
• HEC-HMS / HEC-RAS / EPA SWMM — Hydrology, Hydraulic and Drainage AnalysisCatchment flood flow calculation, flow analysis in pipes and open channels (open channel flow), water surface profiles and backwater effects, and retention pond design to local authority criteria and international standards.
• Main reference standardsACI 318 (concrete) · ACI 562 (existing concrete structures) · ACI PRC-360 (slabs-on-ground) · ACI PRC-351.3 (machine foundations) · AISC 360 (steel) · AASHTO LRFD and AASHTO MBE (bridges) · DPT 1311-50 (wind load) · DPT 1301/1302-61 (seismic) · BS 5975 (temporary shoring) — the edition used is stated in each project's calculation report.

Project types SPN designs

• Residential and commercial buildings, condominiumsRC and steel structural design from single-story detached houses to multi-story high-rise buildings, certified by a licensed engineer for building-permit submissions.
• Factories, warehouses and industrial estatesSteel portal frame design, factory floors for racks and forklifts, machine foundations, drainage and utilities, designed for machinery loads and vibration.
• Solar farms and solar rooftopsCapacity checks of existing roofs, mounting structure design, and flood and fill-level studies for the project site, working together with solar farm pile testing.
• Bridges, roads, box culverts and piersDesign to AASHTO LRFD and Department of Highways standards, and load capacity assessment of existing bridges or piers before increasing vehicle loads.
• Special structures — tank farms, silos, towers, pipe racksDesign for special loads such as liquid pressure, wind and seismic forces, analyzed by FEM in ANSYS.
• Extensions, change of use and disputesRemaining capacity assessment, CFRP / steel jacketing strengthening design, and Expert Witness reports for legal disputes.