Post-tensioned Concrete Haunched Slab Bridge Standards
Complete Phase 1 Report
User's Manual for
PT Slab sample
details (Download a zipped set - 13 sheets; Microstation
The Kansas Department of Transportation has developed standards for the design
and construction of post-tensioned concrete haunched slab bridges. KDOT
currently has standards for reinforced concrete haunched slabs from 12 m (39
ft) to 22 m (72 ft) center span range. Post-tensioned concrete haunched slabs
standards will extend the span range capabilities of the shallow-depth slabs
from 20 m (66 ft) to 28 m (92 ft), in addition to providing a high performance
type bridge superstructure.
The slab bottom (soffit) has a parabolic profile with minimum depth at mid-span
and maximum depth at pier. Longitudinal post-tensioning tendons are draped in a
parabolic profile, which provide primary resistance to the loads. A nominal
prestressing is provided in the transverse direction using straight tendons for
distribution of loads and confinement. Nominal mild steel reinforcing is
provided in both directions, at the top and bottom of slab, for temperature and
shrinkage as well as to assist in the placement of the post-tension tendons.
Spans and Roadways
Four (4) span arrangements will be available in a continuous three (3) span
| Group A
|| 15 – 20 – 15 m (
| Group B:
|| 17 – 22 – 17 m (
| Group C:
|| 19 – 25 – 19 m (
| Group D:
|| 21.5 – 28 -- 21.5
m ( 71-92-71 ft.)
Five (6) roadways will be available for each span group:
| 8.6 m ( 28 ft.)
|| 9.8 m ( 32 ft.)
|| 11.0 m ( 36 ft.)
|| 12.2 m ( 40 ft.)
||40 ft. OS
|| 13.4 m ( 44 ft.)
Concrete Dead Load = 22.8 kN / m3 ( 145 pcf)
Traffic Barrier Load = 4.0 kN / m ( 275 plf ) per rail
Future Wearing Surface = 1.2 kPa ( 25 psf )
Live load design is accompanied by a corresponding allowable concrete tensile
3 * f'c^0.5 maximum tension for HL-93 Loads (LRFD).
The superstructure is designed to satisfy current AASHTO LFD (Load Factor
Design) and the future AASHTO LRFD (Load Resistance Factor Design) design
The goal of design load rating for the given span ranges, governed by the
standard HS-20 Truck among all seven (7) Kansas load rating trucks, is 1.10.
The design of "larger" span groups C and D spans results in a minimum
1.10 rating for the HS-20 truck.
The design of "smaller" span groups A and B spans results in a minimum
1.10 rating for the HS-20 Truck for maximum positive and negative moments, and
a minimum 1.05 rating for negative moment near mid-span of the exterior spans.
Load rating table shown on plans complies with HS-20 for Operating, Inventory and H.E.T. for operating.
An example of a 30 degrees skewed structure is available
for download as reference material. Below is a partial list of considerations for skewed post-tensioned haunched slab bridges.
- Longitudinal post-tensioning details
are expected to be substantially unchanged.
- Transverse post-tensioning
details will require modifications to accommodate skew and potential
conflict with rail post reinforcement.
- Anchor end recess will also
require special details to accommodate the skew.
The current standards for post-tensioned concrete haunched slabs are limited to
three (3) continuous span arrangement. Unlike the standards for the
conventional reinforced concrete haunched slabs, post-tensioned concrete slab
design cannot be extended to multi-span application in a straightforward
manner. The additional length of tendons results in increased loss of
prestress, which may require additional prestress. KDOT may, in the future,
develop standards for multi-span applications. In any event, the maximum total
length of post-tensioned concrete slab bridges, without introducing a strand
splice or interior span joints, is expected to be about 180 m ( 600' ).
The standards are available in three components:
The user's Manual – PDF file format
Plan standards – Microstation ".dgn" drawing file format
Project Special Provisions ( Construction specifications for post-tensioned
concrete haunched slab bridges ) – Microsoft Word file format
Kansas Department of Transportation
Bureau of Design - State Bridge Office
Dwight D. Eisenhower State Office Building
700 SW Harrison Street
Topeka, KS 66603-3754
Attention: Mr. Loren Risch, PE
– Bureau Chief
Mr. Terry Fleck
, PE – Assistant Bureau Chief
PB Booker Associates Inc. ( Consultant )
225 N. Market, Suite 350
Wichita, Kansas 67202
Attention: Mr. Raja Govindaswamy, P.E. – Engineering Manager