Structural Design (Where Most Projects Actually Fail)

Structural design is one of those things people assume happens automatically when building. Architect draws building, engineer makes sure it stands up, done. Reality is way messier—structural design is where fundamental decisions get made about how building actually works, and getting it wrong creates problems that haunt project forever.

I see structural failures regularly. Not dramatic collapses—those are rare. But chronic issues from inadequate structural design: excessive deflection causing cracked finishes, vibration problems, differential settlement, insufficient capacity requiring later reinforcement. These problems cost far more to fix than proper initial structural design would have cost.

What Structural Design Actually Is

Structural design is figuring out how to make building stand up and carry loads safely. Sounds simple but involves complex analysis of forces, material properties, failure modes, construction methods. Not just calculating beam sizes—it’s comprehensive system design.

Loads come from multiple sources. Dead load is weight of building itself—structure, finishes, permanent equipment. Live load is occupancy—people, furniture, stored materials. Environmental loads include wind, seismic forces where applicable, temperature effects. All these need to be considered in design.

Load paths are how forces transfer through structure to foundation. Clear load paths are essential—every element needs to transfer its loads to supporting elements below, ultimately to foundation and ground. Interrupted load paths or inadequate connections cause failures.

The Analysis Part

Structural analysis determines internal forces and stresses in members under applied loads. For simple structures this might be hand calculations. Complex structures need computer analysis—finite element models, dynamic analysis, whatever’s appropriate for situation.

But analysis is only as good as assumptions that go into it. Wrong load estimates, incorrect support conditions, material properties that don’t match reality—any of these make analysis results meaningless. Engineering judgment is knowing what to analyze and how to interpret results.

When Buildings Don’t Need Structural Engineers

Thai regulations require structural engineer for buildings over certain size or complexity. But there’s gray area where building is simple enough that experienced builder can handle structure without formal engineering.

Single-story house with typical span lengths, standard construction methods, normal loading—this can often be built competently without structural engineer using standard details and proven practices. Builders here have built countless similar structures that perform adequately.

But even simple buildings benefit from engineering when there’s anything non-standard. Longer spans than typical, heavier loads, unusual materials, difficult soil conditions—these situations where engineering analysis prevents problems.

Risk is builders sometimes extend their experience beyond where it’s valid. “We’ve always done it this way” works until it doesn’t. I’ve seen undersized structures that deflect excessively, overloaded members that are marginal, inadequate foundations that settle—all from building without engineering for situations that needed it.

The Legal Liability Issue

Beyond technical adequacy, there’s legal aspect. If building has structural problems and there’s no engineer’s stamp on plans, liability falls on whoever built it. Owner might have difficulty with insurance claims, selling property, or legal recourse if problems occur.

Engineer’s professional liability insurance covers structural failures within their design scope. This protection has value even if you’re confident builder knows what they’re doing.

Material Selection And Structural Performance

Different materials have very different structural properties. Concrete is strong in compression but weak in tension—hence reinforcement needed. Steel is strong in both tension and compression but expensive. Wood is good strength-to-weight but vulnerable to moisture and termites here.

Material choice affects not just structural adequacy but constructability, cost, durability, maintenance. Reinforced concrete is common here because materials are available, labor is skilled in concrete work, and it handles tropical climate reasonably well.

Steel framing is used for longer spans, lighter weight, faster construction. But needs corrosion protection in coastal environment, requires welding or bolting skills, costs more than concrete typically. Good for certain applications, not universal solution.

Timber framing is less common for primary structure here than in some regions. Termites, moisture, cost of quality timber—all work against wood structures. Sometimes used for roof framing or specialized applications, but concrete and steel dominate for main structure.

Hybrid Systems

Often best solution is combining materials—concrete foundations and columns for durability and compression strength, steel beams for long spans, wood or metal for roof framing. This uses each material where its properties are advantageous.

But hybrid systems need proper connections between different materials. Concrete-to-steel connections, wood-to-concrete, whatever the interface—these need engineering attention because different materials behave differently and connections are stress concentration points.

Foundation Design Criticality

Foundation is most critical structural element because it’s expensive to fix after construction and failure causes serious problems. Yet foundation design often gets inadequate attention—people focus on visible parts of building and shortchange what’s below ground.

Soil conditions vary enormously in Koh Samui. Decomposed granite hillsides, coastal sand, valley clay, fill material—each has different bearing capacity and settlement characteristics. Can’t use same foundation design everywhere.

Geotechnical investigation determines actual soil properties. Borings or test pits, laboratory testing of soil samples, engineering analysis of bearing capacity and settlement. This costs money but prevents using wrong foundation type for conditions.

Foundation Types

Shallow foundations—spread footings, mat slabs—work where soil has adequate bearing capacity near surface. Economical and simple but only appropriate for competent soil.

Deep foundations—driven piles, drilled piers—bear on deeper, stronger soil layers. Needed where surface soil is weak or for heavily loaded structures. More expensive but necessary in marginal soil conditions.

I’ve seen buildings on inadequate foundations—shallow footings in weak soil that should have had piles. These settle differentially, causing cracks throughout structure. Fixing means underpinning—jacking up building, installing adequate foundations underneath. Extremely expensive and disruptive compared to doing it right initially.

Lateral Load Resistance

Vertical loads get attention—making sure structure doesn’t collapse under weight. Lateral loads—wind, seismic—sometimes get less attention but are critical for structural integrity.

Wind loads in tropical climate can be substantial during storms. Building needs lateral bracing system to resist these loads—shear walls, moment frames, braced frames, whatever’s appropriate for building type and architecture.

Without adequate lateral system, building can rack and deform under wind loads. This might not cause immediate collapse but damages finishes, creates cracks, compromises weather resistance, shortens building life.

Seismic design is less critical in Thailand than in some regions—not a high seismic zone. But some level of lateral resistance is still prudent. Structures that are too flexible or lack any lateral bracing system can have problems even in low seismic conditions.

Tying It Together

Lateral load resistance requires entire structure work as system. All elements need to be connected adequately so forces transfer through structure. Weak connections break this system and cause failures.

Hurricane straps connecting roof to walls, wall-to-foundation connections, column-to-beam connections—all need adequate strength and proper installation. These “small” details are critical for lateral performance.

Deflection Control

Meeting strength requirements isn’t sufficient—structure also needs to be stiff enough that deflections don’t cause problems. Excessive deflection cracks finishes, causes doors and windows to bind, creates uncomfortable floors that feel bouncy or vibrate.

Deflection limits are typically more restrictive than strength requirements. Structure might be strong enough but deflect too much. This is common with cost-optimized designs that minimize material—structure is safe but performs poorly from serviceability standpoint.

Long-span floors are particularly sensitive to deflection and vibration. Span-to-depth ratios need to be conservative enough for acceptable performance. Sometimes this means larger members or closer spacing than pure strength analysis would require.

Connection Design

Connections between structural members are critical and often overlooked. Members might be sized adequately but fail at connections if those aren’t designed properly.

Concrete structures need adequate reinforcement lapping and anchorage. Too-short lap lengths, insufficient development length, inadequate hooks—these cause connection failures. Construction errors in reinforcement placement compound design issues.

Steel connections need proper weld size and quality, or adequate bolt quantity and strength. Field welding quality can be questionable—need inspection and testing to verify. Bolted connections are more reliable but need proper installation torque and hardware.

Construction Coordination

Structural connections often involve coordination between trades. Embed plates for steel-to-concrete connections need to be cast in correctly during concrete placement. Blockouts for MEP penetrations need to be located where they don’t compromise structure.

This coordination requires structural engineer involvement during construction, not just providing drawings upfront and disappearing. Reviewing submittals, answering contractor questions, inspecting critical work—all part of ensuring structure gets built as designed.

The Tropical Climate Factor

Structural design here needs to account for climate effects beyond just loads. Concrete curing in hot humid conditions, corrosion of reinforcement and steel, thermal expansion and contraction, deterioration from moisture and salt exposure.

Concrete mix design needs to be appropriate for exposure—adequate cement content, low water-cement ratio, proper curing. Rushing concrete work in hot weather without adequate curing produces weak concrete that doesn’t achieve design strength.

Steel reinforcement needs adequate concrete cover to prevent corrosion. Specified minimum cover isn’t suggestion—it’s critical for durability. Inadequate cover in coastal exposure means accelerated corrosion and spalling concrete within years.

Expansion Joints

Thermal movement in tropical climate is significant—large temperature differentials between day and night, hot sun on exposed surfaces. Concrete and masonry structures need expansion joints to accommodate movement without cracking.

Expansion joint spacing and detailing is part of structural design. Too far apart and structure cracks between joints. Joints need proper detailing—sealants, backer rods, flashing—or they leak and defeat their purpose.

Cost Optimization Versus Safety

There’s always pressure to minimize structural costs—less concrete, smaller steel, cheaper foundations. This is reasonable optimization up to point. But taken too far, it compromises safety or performance.

Structural engineer’s job includes finding economical solutions but not at expense of adequacy. Safety factors exist for reason—accounting for unknowns, construction variations, material property scatter, unforeseen loads.

Minimum code-compliant design is starting point, not necessarily optimal solution. For important structures or difficult conditions, designing above minimum code requirements provides better long-term performance.

False economy is reducing structural costs but creating problems requiring expensive repairs later. Or worse, building that performs marginally and makes occupants uncomfortable even though it’s technically safe.

Value Engineering

Legitimate value engineering finds less expensive ways to achieve same performance—different materials, alternative framing schemes, whatever reduces cost without compromising function.

But “value engineering” sometimes becomes excuse for just reducing capacity until it barely meets minimum requirements. This isn’t adding value—it’s cost-cutting that reduces quality and performance.

Renovation And Existing Structure Evaluation

Renovating existing buildings requires evaluating existing structure to determine what it can support and what modifications are feasible. Can’t just assume existing structure is adequate for new loads or alterations.

This means investigating existing construction—what materials were used, what sizes are members, how are things connected, what’s the condition. Sometimes requires invasive investigation—removing finishes to inspect structure, taking concrete samples for strength testing.

Adding loads to existing structure—new floor, heavier use, additional equipment—requires verifying existing capacity is adequate. Often it’s not, requiring reinforcement or supplementary structure.

Seismic Retrofit

While Thailand isn’t high seismic zone, some older buildings lack even basic lateral bracing. Retrofitting for better lateral performance during major renovation makes sense—adding shear walls, strengthening connections, improving foundation anchorage.

This is opportunity when building is opened up for renovation anyway. Adding lateral bracing to occupied building without major disruption is difficult and expensive.

Documentation And Record Drawings

Structural design needs to be documented—drawings showing member sizes, connection details, specifications for materials and construction. This documentation is necessary for construction, permitting, and future reference.

As-built drawings reflecting what actually got constructed are valuable for building owners. Design might show one thing but field conditions or changes result in different construction. Documenting what actually exists helps future renovation or modification efforts.

Many older buildings lack adequate structural documentation. Nobody knows what size reinforcement is in concrete or how connections were made. This makes renovation difficult because existing capacity can’t be verified without expensive investigation.

Common Structural Design Mistakes

Undersizing members is obvious mistake but surprisingly common. Pressure to reduce costs, errors in calculations, underestimating loads—various causes but result is inadequate structure.

Inadequate connection design means members might be sized okay but connections fail. This is particularly problematic because connection failures can be sudden and catastrophic versus gradual overload of members.

Ignoring serviceability means structure might be safe but performs poorly—excessive deflection, vibration, cracking. Technically meets code but creates problems for occupants.

Poor detailing creates construction difficulties or weak points. Structure might work in theory but details that are unbuildable or don’t function as intended in practice.

The Review Process

Having another engineer review structural design catches mistakes and improves quality. Fresh perspective sees things original designer missed. Code requires this for certain building types but it’s good practice even when not required.

Our Structural Design Approach

At CJ Samui Builders, we work with qualified structural engineers for all projects requiring structural design. This includes new construction beyond simple standard designs, renovations involving structural changes, and evaluation of existing structures.

Our approach emphasizes understanding actual conditions through adequate investigation, designing for both safety and serviceability not just minimum code compliance, and detailed coordination between structural design and architectural intent.

We’ve seen too many structural problems from inadequate design—buildings that work marginally or require expensive repairs, structures that don’t perform as intended, foundations that settle. These problems are preventable through proper structural design upfront.

Our structural design services are integrated with construction process—not just providing drawings but staying involved through construction to ensure proper execution. Because structural design on paper means nothing if it doesn’t get built correctly. And building it correctly requires understanding design intent and having oversight during construction.

Structural adequacy is fundamental to building performance and longevity. It’s not glamorous part of construction—nobody sees structural members once building is finished. But it’s what makes building safe, durable, and functional for decades. Shortchanging structural design to save modest costs upfront creates risks and problems that far exceed those savings.