The Bridge Enginerd

Prestress  ·  Design  ·  Analyze  ·  Build

Bridge design,
worked out.

Free AASHTO LRFD design tools that show every step of the calculation, a forum for real bridge engineering questions, and videos that explain the why behind the code.

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Prestressed girder · flexural strength AASHTO 5.6.3

AASHTO Type IV · 100 ft span · 44 strands · Aps = 6.732 in²

  1. Stress in strandsfps = fpu (1 − k c / dp) = 261.76 ksi
  2. Depth to neutral axisc = Aps fps / (0.85 f′c β1 b) = 6.35 in
  3. Depth of stress blocka = β1 c = 5.40 in
  4. Nominal resistanceMn = Aps fps (dp − a / 2) = 8,160.8 kip-ft
  5. Factored resistanceMr = φ Mn = 1.00 × 8,160.8 = 8,160.8 kip-ft
  6. Strength I momentMu = 6,494.3 kip-ft

PASSMu / Mr = 0.796

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Design tools

Twelve free calculators, every number shown

Each tool follows the published method, checks every limit state and walks through the full hand calculation: formula, numbers, result and code clause.

Concrete

Prestressed girder

Strand pattern, losses, transfer and service stresses, strength, shear, end bars and camber.

AASHTO 5.9 · 5.7 Steel

Steel beam

Finds the lightest W-shape, then checks strength by segment, the deck pour, fatigue, deflection and studs.

AASHTO 6.10 · A6 Concrete

Deck slab

Table A4-1 moments with strength, minimum steel, crack control, distribution and temperature steel.

AASHTO A4-1 · 5.6.7 Loads

Load rating

LRFR design, legal and posting ratings for moment and shear, with condition and system factors.

MBE 6A Bearings

Elastomeric bearing

Method B: shape factor, shear strains, stability, shims and anchorage.

AASHTO 14.7.5 Planning

Bridge layout

Stations of every fill face, bent and bearing, with precast girder lengths for any number of spans.

MoDOT EPG 751.22
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From inputs to a calc package

Check it, learn it, print it

  1. 1

    Enter your bridge

    Results update as you type, with every check shown as a ratio so you can see what governs.

  2. 2

    Read the hand calcs

    Open the hand calculations to follow each step in plain language, with the AASHTO article beside it.

  3. 3

    Print the calc

    Add your project details and print a free explanation calc with a header box on every sheet. A concise professional calc sheet is coming soon.

Discussions

Questions from real practice

A forum for bridge and structural engineering: load rating and AASHTOWare, LRFD design, prestressed and steel girders, inspection, construction and the exam path. Ask, answer and mark the replies that helped.

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Videos

Watch the calculation

The same topics, walked through on YouTube, for when it's easier to see a calculation done than to read it.

The Bridge Enginerd on YouTube

Who's behind it

Built by Nirav Khanal

Founder, The Bridge Enginerd

An Engineer Intern (E.I.) in Missouri and a structural designer working in bridge design: prestressed girder superstructures, more than 200 MoDOT load ratings and bridge inspection. The Bridge Enginerd is where the calculations behind that work are made easy to see and check.

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