POTENTIAL ISSUE TEAM STUDIES
CONCRETE CODIFICATION OPPORTUNITIES
1. CONCRETE SHEAR WALLS
Current Codes provide detailed provisions for the seismic design based
on flexural performance considerations. Yet tests on shear walls show
that even for hw/lw ratios of 3.0, 30% of the shear wall lateral deformation
is due to shear deformations. Many shear walls have proportions that
result in their performance being controlled by shear, rather than flexural,
considerations. For both empirical and performance based design
provisions are needed for the detailing walls that are shear controlled.
POTENTIAL ISSUE TEAM STUDIES
CONCRETE CODIFICATION OPPORTUNITIES
2. ANCHORAGE TO CONCRETE
The current design requirements for anchoring to concrete
are more complex than necessary for many situations and
are not well validated for earthquake loading situations. A
proposal for unifying the ACI 318 and ASCE 7 provisions for
earthquake loading is currently under consideration within
ACI 318. However, more work is needed. A distinction is
warranted between requirements where the loss of a single
anchorage has significant structural implications and that
where redundancy reduces that structural significance . For
seismic applications a distinction is also warranted between
requirements for small anchors ( 3/16th ϕand less ) and those
for anchors of larger sizes and between anchors carrying
significant forces and those carrying nominal forces only.
POTENTIAL ISSUE TEAM STUDIES
CONCRETE CODIFICATION OPPORTUNITIES
3. TILT-UP CONSTRUCTION AND INTERMEDIATE PRECAST WALLS
Design requirements for tilt-up wall systems are based primarily on data
for older wall systems with plywood roofs. Modern tilt-up construction
uses other roofing systems and in seismic areas walls are connected to
foundations using systems not envisaged by current codes. Seismic
requirements for tilt-up with varying SDCs need clear delineation for:
diaphragms; anchorage of diaphragms to walls; wall design; and wall to
foundation connections. Correlation of the performance of tilt-up
construction in recent earthquakes, as measured by strong motion
recordings, and design provisions needs study.
POTENTIAL ISSUE TEAM STUDIES
CONCRETE CODIFICATION OPPORTUNITIES
4. PILES AND DRILLED PIERS
Seismic design requirements for the body of concrete piles and drilled
piers need to be updated consistent with the results of research.
Requirements for the anchorage of piles to pile caps, footing beams and
mats need to be better defined for varying SDCs. Requirements for
prestressed footing beams and mats need to be defined.
POTENTIAL ISSUE TEAM STUDIES
CONCRETE CODIFICATION OPPORTUNITIES
5. USE OF HIGH STRENGTH MATERIALS
Studies and code provisions are needed for the use of high strength
concrete materials in seismic applications Deformed reinforcing bars are
available with yield strengths up to 110 ksi and good ductility. ACI 318
limits steel yield strengths for longitudinal and shear reinforcement to 75
ksi. Steels with strengths up to 100 ksi can be used as confinement
reinforcement. While ACI 318 places no limit on normalweight concrete
strengths that can be used in seismic applications most seismic
provisions have been developed using concrete strengths of 6 ksi or less.
POTENTIAL ISSUE TEAM STUDIES
CONCRETE CODIFICATION OPPORTUNITIES
6. LIGHTWEIGHT CONCRETE
ACI 318 defines lightweight concrete as concrete having an equilibrium
density between 90 and 115 lbs/ft3. Specified compressive strength for
lightweight concrete in seismic applications is essentially limited to 5ksi.
However, lightweight concrete with strengths up to 16,000 psi at 90 days
can readily be produced using current lightweight aggregates
POTENTIAL ISSUE TEAM STUDIES
CONCRETE CODIFICATION OPPORTUNITIES
7. INSULATED CONCRETE WALL PANELS
Insulated concrete walls created using precast sandwich panels or
stay in place forms are increasingly used for energy conservation
reasons. Limitations to the use of such panels for seismic resistance
or in seismic applications needs to be better defined.
POTENTIAL ISSUE TEAM STUDIES
CONCRETE CODIFICATION OPPORTUNITIES
8. PRECAST PRESTRESSED CONCRETE DIAPHRAGMS
Precast prestressed concrete diaphragms are a common floor systems
in concrete parking garages. Many such garages were badly damaged
in the 1994 Northridge earthquake. Over the past decade the precast
industry has invested heavily in the development of methods to ensure
better performance of precast garages. The improved performance
requires modification of both prescribed design forces and product
details. Coherent codification of those modifications is needed.