Jul. 15, 2024
Hardware
Are you interested in learning more about post tension anchor? Contact us today to secure an expert consultation!
Complete Phase 1 Report
for Standard Details
PT Slab sample details
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.
Four (4) span arrangements will be available in a continuous three (3) span configuration.
Group A:15 - 20 - 15 m (50-65-50 ft.)Group B:17 - 22 - 17 m (55-72-55 ft.)Group C:19 - 25 - 19 m (62-82-62 ft.)Group D:21.5 - 28 - 21.5 m ( 71-92-71 ft.)Six (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 stress limitation.
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 specifications.
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.
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:
Kansas Department of Transportation
Bureau of Structures and Geotechnical Services
Dwight D. Eisenhower State Office Building
700 SW Harrison Street
Topeka, KS -
: 785-296-
Attention: Mr. Mark Hoppe, Bureau Chief
or Mr. John Jones, Assistant Bureau Chief
PB Booker Associates Inc. ( Consultant )
225 N. Market, Suite 350
Wichita, Kansas
: 316-263-
Attention: Mr. Raja Govindaswamy, P.E. - Engineering Manager
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS
Log In
For more post tension system solutionsinformation, please contact us. We will provide professional answers.
Related links:Are you an
Engineering professional?
Join Eng-Tips Forums!
*Eng-Tips's functionality depends on members receiving . By joining you are opting in to receive .
Promoting, selling, recruiting, coursework and thesis posting is forbidden.
Eng-Tips Posting Policies
Maximum Pour size for PT slab?
thread507- Forum Search FAQs Links MVPsForum
Search
FAQs
Links
MVPs
(Civil/Environmental)
(OP)
24 May 20 10:48Hello everyone! A simple question abound the maximum allowed pour area for post tensioned slab and what maximum length is allowed for PT slabs without pour strip.
(Structural)
24 May 20 12:15The maximum pour size is determined by site logistics how many concrete trucks the contractor can get to site before they need to stop. The maximum I've experienced is m3 in a day
For tendon lengths, about 30m for a band beam, 40m for a slab tendon. If you use double live end tendons you can go about double that, but pour sizes may become impractical. Minimum tendon length of about 6m, otherwise losses from wedge draw in become excessive.
(Structural)
24 May 20 21:39999's numbers on tendon lengths would be for unbonded tendons. We would normally recommend about 25% less for bonded tendons due to the higher friction.
At 80m slab length you would need to look closely at shortening effects on columns near the edges and restraint effects on the slab.
RE maximum volume of pour, the pour size is also controlled by the surface area that needs to be finished. That would depend on local building practice.
(Structural)
25 May 20 15:08RAPT,
I know I'm based on the US where unbonded tendons is common practice, however, based on the OP's previous posts I assumed he was referring to bonded tendons and so the maximum tendons length I provided were based on PTIA's 'Practical Pretress Detailing' - are you recommending the values in this document should reduced by 25%?
999
(Structural)
25 May 20 21:01Yes, 40m single end stress and 80m double end stress is not recommended.
Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.
Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.
Click Here to join Eng-Tips and talk with other members! Already a Member? Login
If you are looking for more details, kindly visit wholesale post tension wedges.
Previous: Why use post tension wedges?
Next: Is your Concrete Safe? Learn How Post Tensioning Wedges Prevent Structural Failures
If you are interested in sending in a Guest Blogger Submission,welcome to write for us!
All Comments ( 0 )