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Steel Joist Spacing Calculator

Open-Web Steel Joist Design per SJI 100-2025 • ASCE 7-22 • IBC 2024 • ASD & LRFD

K-Series LH-Series DLH-Series KCS-Series Real-Time Free
Preset:
Geometry
ft
Span exceeds series maximum.
4.0 ft
ft
ft

Edge offset = half spacing assumed at each end.

Loads
psf
50 psf
psf
psf
psf
kips
ft

Joist self-weight is included automatically.

Joist Selection
$/ton
📈 Results ✓ PASS
Designation
--
--
Actual Spacing
--
ft o.c.
Joist Count
--
total joists
Seat Reaction
--
kips per end
Max Moment
--
kip-ft
LL Deflection
--
in (L/--)
TL Deflection
--
in (L/--)
Total Steel Wt
--
lbs
Est. Cost
--
USD (material)
Req. Camber
--
inches
Trib. Area/Joist
--
ft²
Governing Check
--
limit state
Utilization Ratios
Moment (UR)
0%
Shear (UR)
0%
LL Deflection
0%
TL Deflection
0%
📋 Joist Layout Plan View
📈 Joist Elevation & Deflection Diagram

⚠ Bridging Requirements (SJI 100-2025)

    Series Comparison (Same Loading)
    Designation Series Depth (in) Wt/ft (plf) Moment UR LL Defl. Steel Wt (lbs) Est. Cost Status

    ✓ Code Compliance Summary

    Geometry & Joist Count

    Number of joists across bay width (N), with edge offset = half spacing:

    \[ N = \left\lceil \frac{W - 2 \cdot e}{s} \right\rceil + 1 \]

    Adjusted actual on-center spacing:

    \[ s_{\text{actual}} = \frac{W - 2 \cdot e}{N - 1} \]

    where W = bay width (ft), e = edge offset (ft), s = target spacing (ft)

    Tributary & Design Load

    \[ w = (DL + LL + S) \times s_{\text{actual}} \quad \text{[plf]} \] \[ w_{LL} = LL \times s_{\text{actual}} \quad \text{[plf]} \]

    where DL, LL, S = dead, live, snow load in psf; s = spacing in ft

    Bending & Shear (Simply Supported, Uniform Load)

    \[ M_{\max} = \frac{w L^2}{8} \quad \text{[kip-ft]} \] \[ V_{\max} = \frac{w L}{2} \quad \text{[kips]} \]

    where w = distributed load (klf), L = span (ft)

    Equivalent Uniform Load (EUL) for Point Load

    \[ \text{EUL} = \frac{8 \cdot P \cdot a \cdot (L - a)}{L^2} \]

    where P = point load (kips), a = distance from support to load (ft), L = span (ft)

    Deflection

    Midspan deflection for uniformly distributed load:

    \[ \Delta = \frac{5 \, w \, L^4}{384 \, E \, I_{\text{eff}}} \]

    Live load deflection check:

    \[ \frac{\Delta_{LL}}{L} \leq \frac{1}{360} \quad \text{(floors)}, \quad \frac{1}{240} \quad \text{(roofs)} \]

    E = 29,000 ksi (steel); Ieff from SJI published tables per designation

    Utilization Ratios

    \[ UR_M = \frac{M_{\text{actual}}}{M_{\text{allow}}} \leq 1.0 \] \[ UR_V = \frac{V_{\text{actual}}}{V_{\text{allow}}} \leq 1.0 \] \[ UR_{\Delta,LL} = \frac{\Delta_{LL}}{\Delta_{\text{allow}}} = \frac{\Delta_{LL}}{L/\text{limit}} \leq 1.0 \]

    Joist Seat Reaction & Material

    \[ R = \frac{w \cdot L}{2} \quad \text{[kips per end]} \] \[ W_{\text{steel}} = \text{wt/ft} \times L \times N_{\text{joists}} \quad \text{[lbs]} \]

    Recommended camber (SJI standard):

    \[ \delta_{\text{camber}} = \frac{5 \, w_{DL} \, L^4}{384 \, E \, I_{\text{eff}}} \]

    Camber set to counteract dead load deflection only.

    LRFD Load Combination

    \[ w_u = 1.2 \, DL + 1.6 \, LL + 0.5 \, S \] \[ M_u = \frac{w_u L^2}{8}, \quad \phi M_n \geq M_u, \quad \phi = 0.9 \]
    Disclaimer: This tool is for preliminary estimation and educational purposes only. Results are based on simplified SJI load table approximations and standard beam theory. All structural designs must be reviewed and stamped by a licensed Structural Engineer. Verify against current SJI 100-2025, ASCE 7-22, and applicable local building codes before construction.

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