THE CONCRETE BRIDGE MAGAZINE

SPRING 2016

ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.

Issue link: http://www.aspiremagazinebyengineers.com/i/657823

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F H WA 36 | ASPIRE Spring 2016 P ost-tensioning (PT) has increased the str ength and ser vicea bility for many of our nation's bridges and will continue to play an important role in the design of f u t u r e b r i d g e s . I n - s e r v i c e p o s t - t e n s i o n e d b r i d g e s h a v e p r o v e n t o b e v e r y d u r a b l e , however given the significant contribution t h a t P T t e n d o n s p r o v i d e t o t h e b r i d g e 's load-carr y capacity, there is great interest i n a s s e s s i n g t h e i r i n - s e r v i c e c o n d i t i o n . I n s p e c t i o n o f P T s t r a n d s c a n b e d i f f i c u l t due to their multiple layers of encasement, w h i c h t y p i c a l l y i n c l u d e g r o u t , d u c t s , r einfor cing steel, and str uctural concr ete (Fig. 1). N o n d e s t r u c t i v e e v a l u a t i o n ( N D E ) t e c h n o l o g i e s p r o v i d e t h e b e s t t o o l s a n d t e c h n i q u e s t o a s s e s s t h e c o n d i t i o n o f P T tendons. NDE technologies ar e advancing r a p i d l y a n d a r e o f f e r i n g i n c r e a s e d assessment capability and por tability. Past PT NDE research has focused primarily on choosing the appropriate NDE technology f o r t h e a p p l i c a t i o n , w h i c h m a n y t i m e s h a s r e d u c e d t h e e f f e c t i v e n e s s o f t h e N D E t e c h n o l o g y. T h e F e d e r a l H i g h w a y A d m i n i s t r a t i o n ( F H WA ) h a s i n i t i a t e d r e s e a r c h t a s k e d t o d o t h e r e v e r s e , w h i c h i s t o d e s i g n a n d d e t a i l t h e b r i d g e t o accommodate the NDE technology in order to maximize the effectiveness of the most promising tools. Research Goals T h e p r i m a r y g o a l o f t h i s r e s e a r c h i s t o r e d u c e t h e l i k e l i h o o d o f p r e m a t u r e d e t e r i o r a t i o n o f p o s t - t e n s i o n e d b r i d g e c o m p o n e n t s a n d s y s t e m s b y i d e n t i f y i n g i s s u e s e a r l y t h r o u g h t h e u s e o f N D E a n d p r o v i d e b e t t e r i n f o r m a t i o n a b o u t l o a d - c a r r y i n g c a p a c i t y. T h i s r e s e a r c h w i l l d e v e l o p g u i d a n c e f o r t h e d e s i g n a n d d e t a i l i n g o f p o s t - t e n s i o n e d b r i d g e s a n d tendon components to facilitate application o f p r o m i s i n g N D E m e t h o d s . T h e e f fo r t i s focused on evaluation of grouted internal a n d e x t e r n a l P T s y s t e m s . T h e u l t i m a t e g o a l i s t o f i n d c o m b i n a t i o n s o f N D E , P T system details, and bridge superstr uctur e details, that can be implemented into future structures to increase the reliability and ease of inspection for post-tensioned systems. Research Approach T h e f i r s t t a s k f o r t h i s r e s e a r c h w a s t o i d e n t i f y p r o m i s i n g a n d r e a d i l y a v a i l a b l e N D E t e c h n o l o g i e s w i t h t h e a b i l i t y t o d e t e c t s t r a n d c o r r o s i o n , g r o u t v o i d s / c o n d i t i o n , a n d r e m a i n i n g p r e s t r e s s . N o o n e N D E t e c h n o l o g y c a n d e t e c t a l l t h e p o s s i b l e i s s u e s , h o w e v e r m a n y c a n a c c u r a t e l y d e t e c t o n e o r m o r e . E a c h o f t h e s e N D E t e c h n o l o g i e s w a s a s s e s s e d o n i t s a b i l i t y t o b e a p p l i e d t o a P T b r i d g e s t r u c t u r e a n d p r o v i d e a c c u r a t e a s s e s s m e n t d a t a . B o t h s t r e n g t h s a n d l i m i t a t i o n s f o r e a c h N D E t e c h n o l o g y w e r e d o c u m e n t e d a l o n g w i t h a n y c u r r e n t u s e i n a s s e s s i n g a n d i n s p e c t i n g P T b r i d g e s . T h e n u m e r o u s p r o m i s i n g N D E t e c h n o l o g i e s i n v e s t i g a t e d a r e l i s t e d b e l o w. • A c o u s t i c e m i s s i o n • E l e c t r i c a l l y i s o l a t e d t e n d o n s • G r o u n d - p e n e t r a t i n g r a d a r • H a l f - c e l l p o t e n t i a l • I m p a c t e c h o • I n f r a r e d t h e r m o g r a p h y • Ra d i o g r a p h y • Ti m e d o m a i n r e f l e c t o m e t r y • U l t r a s o n i c t e s t i n g • V i s u a l i n s p e c t i o n I n a d d i t i o n , t h i s r e s e a r c h i d e n t i f i e d P T s y s t e m c o m p o n e n t s a n d b r i d g e s u p e r s t r u c t u r e d e t a i l s t h a t h i n d e r t h e N D E m e t h o d ' s a b i l i t y t o e f f e c t i v e l y e v a l u a t e t h e P T t e n d o n . U s i n g t h i s i n f o r m a t i o n , p r a c t i c a l d e t a i l s f o r n e w d e s i g n a n d r e c o m m e n d a t i o n s o n h o w t o a l t e r P T s y s t e m c o m p o n e n t s a n d b r i d g e s u p e r s t r u c t u r e e l e m e n t s w i l l b e d e v e l o p e d . A s o n e m i g h t e x p e c t , t h e a p p l i c a b i l i t y a n d a c c u r a c y o f m a n y N D E t e c h n o l o g i e s a r e a f f e c t e d b y t h e t y p e o f Designing Post-Tensioned Bridges to Accommodate Nondestructive Evaluation by Reggie Holt, Federal Highway Administration Figure 1. Typical post-tensioning strand encasement. All Figures and Photos: WSP/Parsons Brinckerhoff.

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