Chapter 5 Conclusions and Recommended Future Research

Several pertinent conclusions were made based on the study described in this report:

1. Based on the results of the withdrawal tests of the two adhesives and using untapped holes, the strength of the Borden adhesive was superior to the Hilti HIT HY 150 adhesive.
2. Tapping of the holes significantly increased withdrawal resistance.
3. Statistically, embedment depth had a significant influence on the withdrawal strength of the Borden adhesive.
4. Statistically, embedment depth had no significant influence on the withdrawal strength of the Hilti HIT HY 150 adhesive.
5. The initial tangent and secant approaches to establishing a slip modulus were not applicable to the slip behavior observed in anchored notch connection due to the predominately linear behavior encountered.
6. Slip moduli for the specimen using Borden adhesive ranged from about 66,000 lb/in to about 219,000 lb/in, with a mean for all specimens of approximately 136,000 lb/in. These values are significantly higher than those typical for slip connections in wood/wood layered systems with nail shear connectors.
7. Statistically, changes in the notch dimensions used in this study for specimens with nominal 2x4 wood members had a significant effect on slip modulus and failure load.
8. Statistically, the changes in the notch dimensions used in this study for specimens with nominal 4x4 wood members had no significant effect on slip modulus and failure load.
9. Various modes of failure were observed in the slip tests, with none predominating.
10. The use of the Hilti HIT HY 150 adhesive provided the best balance of adhesive properties, interlayer strength and slip resistance properties.
11. Concrete consolidation was determined to be critical in achieving a high degree of composite action.
12. Computed efficiency of the composite action of the beam specimens ranged from 54.9 percent to 77.0, the mean was 67.2 percent.
13. Layered beam failures were almost exclusively characterized by tensile failure in the wood.
14. Statistically, the use of nominal 2x4 vs nominal 4x4 wood members had no significant influence on the load performance of the beam specimens.
15. Computed efficiency of the composite action of the skewed and rectangular deck specimens was 81.1 percent and 92.2 percent, respectively. However, these are optimistic as the deck layer was modeled as a solid layer.
16. Lateral load sharing of the bare wood decks was dramatically improved by addition of the concrete layer.

Some recommendations for future research are evident:

1. Pull out tests of the phenol resorcinol adhesive with tapped holes should be performed.
2. Additional slip testing should be performed on specimens having lengths corresponding to the notch spacing, or end distances used for the layered beam and deck specimens.
3. Additional slip testing should be performed on specimens using the Hilti HIT HY 150 Adhesive.
4. Durability if the notched shear key/anchor concept should be examined under cyclic variation of temperature and humidity and repeated loading.
5. Deeper layered beam and deck specimens should be examined to potentially allow for increased bridge span length.
6. Rigorous finite element modeling of the mechanics of the notched/shear key anchor is needed to understand the underlying mechanics of its behavior and examine potential improvements.
7. More rigorous finite element modeling of the layered wood concrete beam and deck specimens is needed to more accurately model the discrete wood members and connection details.

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1995 Annual book of ASTMSTANDAR