Timber Beams

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Complete Attribute Reference

This page documents all available attributes for timber beam calculations. While presets provide sensible defaults, you can override or set any of these attributes explicitly.

For the complete schema definition with all properties, see the API Reference.

Input Validation

All inputs are validated before processing. Invalid inputs return HTTP 400 with detailed error messages:

Code
 
{
  "error": {
    "code": "VALIDATION_ERROR",
    "message": "Input validation failed",
    "details": [
      { "field": "L_X", "message": "Expected number, received string" }
    ]
  }
}

Key validation rules:

• All enum values are case-sensitive (e.g., "Wet" not "wet")
• Numeric fields must be actual numbers, not strings (14 not "14")
• Positive numbers required for lengths, widths, and limits

See Error Handling for detailed examples of common errors and how to fix them.

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Core Attributes

These are the essential attributes for any timber beam calculation.

Geometry

Attribute	Type	Required	Validation	Description
L_X	number	Yes	Must be positive	Beam plan length in feet
supports	array	Yes	Minimum 2 supports	Support definitions. Format: [["Type", position, bearingLength], ...]
n_com	integer	No	Positive integer	Number of plies for multi-ply beams (default: 1)

Supports Format:

Code
 
[
  ["Pinned", 0, 5.5],      // [Type, position_ft, bearing_length_in]
  ["Pinned", 20, 5.5]
]

Each support tuple: [type, position, bearingWidth]

• type - One of: "Pinned", "Roller", "Fixed", "Hinge", "Top Brace", "Bottom Brace" (case-sensitive)
• position - Non-negative number (feet from left end)
• bearingWidth - Positive number (inches)

Member Selection

Attribute	Type	Required	Description
type	string	No	"Database" (default) or "Custom"
member	string	When type=Database	Member designation (e.g., "2x10 D.Fir-L No. 2")

For all available member designations, see List Members.

For Custom Sections:

Attribute	Type	Required	Description
b_input	number	When type=Custom	Member width in inches
d_input	number	When type=Custom	Member depth in inches
species	string	When type=Custom	Wood species/grade

---

Loads

Point & Moment Loads (loadsConc)

Format: ["Label", position_ft, {"LoadType": [force_lb, moment_lb_ft], ...}]

Code
 
"loadsConc": [
  ["Point Load", 10, {"D": [1000, 0], "L": [2000, 0]}]
]

Load Types:

• D - Dead load
• L - Live load (occupancy)
• Lr - Roof live load
• S - Snow load
• W - Wind load
• E - Seismic load

Distributed Loads (loadsDist)

Format varies by use case:

For headers/girders/generic beams (explicit widths):

Code
 
["Label", start_ft, end_ft, trib_width_start_in, trib_width_end_in, {"D": [psf], "L": [psf]}]

For joists only (with spacing reference):

Code
 
["Label", 0, "L", "spacing", "TW_s", {"D": [psf], "L": [psf]}]

Important: Variable references are only supported for joist presets.

The references "L", "spacing", and "TW_s" are only resolved for: floorJoist, ceilingJoist, deckJoist, rafter

For all other presets (genericBeam, floorGirder, floorHeader, etc.), you must use explicit numeric values:

Code
 
// ❌ Won't work for genericBeam - causes validation error
["Floor Load", 0, "L", "spacing", "TW_s", {"D": [15], "L": [40]}]

// ✅ Use explicit numbers
["Floor Load", 0, 14, 16, 0, {"D": [15], "L": [40]}]

Line Loads (loadsLine)

Format: ["Label", start_ft, end_ft, {"LoadType": [plf_start, plf_end], ...}]

Code
 
"loadsLine": [
  ["Wall Load", 0, 20, {"D": [100, 100]}]
]

---

Flitch Plate Options

For steel-reinforced timber beams (flitch plates).

Attribute	Type	Default	Description
flitch	string	"No"	Enable flitch plates: "Yes" or "No"
n_flitch	number	1	Number of steel plates
t_flitch	number	0.25	Plate thickness in inches
d_flitch	number	-	Plate depth in inches
F_y	number	36000	Yield strength in psi

Example:

Code
 
{
  "flitch": "Yes",
  "n_flitch": 2,
  "t_flitch": 0.375,
  "d_flitch": 11,
  "F_y": 36000
}

---

Design Conditions

Service Conditions

Attribute	Type	Default	Valid Values
wet	string	"Dry"	"Dry", "Wet"
T	string	"T ≤ 100°F"	"T ≤ 100°F", "100°F < T ≤ 125°F", "125°F < T ≤ 150°F"
incised	string	"No"	"Yes", "No"

Member Configuration

Attribute	Type	Default	Valid Values
repeat	string	varies	"Non-Repeating", "Repeating"
LTB_bracing	string	varies	"No Continuous Bracing", "Top Braced", "Bottom Braced", "Top & Bottom Braced"
bendingAxis	string	"X-X"	"X-X", "Y-Y"

Load Options

Attribute	Type	Default	Description
incSW	string	"Yes"	Include self-weight: "Yes" or "No"
LLT	string	"Occupancy"	Live load type: "Occupancy", "Storage", or "Impact"
brace_PL	string	"No"	Brace at point loads: "Yes" or "No"
shearDelta	string	"No"	Consider shear deflection: "Yes" or "No"
LL_pattern	string	"No"	Live load patterning (BETA): "Yes" or "No"

---

Deflection Limits

Attribute	Type	Default	Description
Delta_hard	number	2	Absolute deflection limit in inches
Delta_Span_ST	number	360	Short-term deflection limit (L/xxx)
Delta_Span_LT	number	240	Long-term deflection limit (L/xxx)
doubleCantileverDeflection	string	"Yes"	Double limits for cantilevers: "Yes" or "No"

Example - Stricter limits:

Code
 
{
  "Delta_hard": 1.0,
  "Delta_Span_ST": 480,
  "Delta_Span_LT": 360
}

Simplified Deflection

For floor joists and similar applications, IBC requires checking combined dead load plus live load deflection.

Attribute	Type	Default	Description
flag_SD	string	"No"	Consider simplified deflection: "Yes" or "No"
Delta_Span_DL+LL	number	180	Simplified DL+(LL or SL) deflection limit (L/xxx)

When flag_SD is "Yes", the calculator checks the combined DL+LL deflection against the Delta_Span_DL+LL limit in addition to the standard short-term and long-term checks.

Example - Floor joist with simplified deflection:

Code
 
{
  "preset": "floorJoist",
  "attributes": {
    "L_X": 14,
    "member": "2x10 D.Fir-L No. 1",
    "flag_SD": "Yes",
    "Delta_Span_DL+LL": 240,
    "supports": [["Pinned", 0, 3.5], ["Pinned", 14, 3.5]],
    "loadsDist": [["Floor Load", 0, "L", "spacing", "TW_s", {"D": [10], "L": [40]}]]
  }
}

---

Inclined Beam Options

For rafters and sloped members.

Attribute	Type	Default	Description
incline_flag	string	"Horizontal"	"Horizontal", "Simple Slope", "Hip/Corner Slope"
alpha_incline	number	4	Roof pitch (rise per 12 run)

Note: For inclined beams, use the rafter or hipValley preset which includes proper load combination setup.

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Next Steps

• Error Handling - Validation errors and how to fix them
• Examples - Complete calculation examples
• Presets Reference:
  • Joists - Floor, ceiling, deck joists and rafters
  • Beams - Girders, headers, and deck beams
  • Special - Generic and flitch beams, hip/valley
• API Reference - Full endpoint documentation