Wheel loads from highway bridge strains field studies refe
Agarwal, A. C, and Billing, J. R. (1990). "Dynamic testing of the St. Vincent Street
Bridge." Proc. Annual Conf., Canadian Society for Civil Engineering, vol. IV-1,
Bakht, B., and Pinjarkar, S. J. (1990). "Review of dynamic testing of bridges."
Transportation Research Record, 1223, 93-100.
Billing, J. R. (1982). "Dynamic loading and testing of bridges in Ontario, 1980."
Proc, Int. Conf. on Short and Medium Span Bridges, Canadian Society of Civil
Engineering, vol. 1, 125-139.
Cantieni, R. (1983). "Dynamic load tests on highway bridges, 60 years experience
of EMPA." Report No. 271, Swiss Federal Lab. for Mater, and Testing Res.,
Closure by Colin O'Connor6
This paper, together with Chan and O'Connor (1990), O'Connor and
Chan (1988a, b), and O'Connor and Pritchard (1985), form part of a con-
tinuing program of research into bridge-vehicle interaction. At no stage has
it been suggested that observed field values of impact be employed directly
in bridge design. For example, O'Connor and Pritchard (1985) say, "it would
be premature to use these values in design." Rather, the thrust of these
papers has been that these high values of I are surprising and need further
study. The reference to "direct practical significance" in the original paper
was in the context of "the development of the calibrated design vehicle."
Indeed, the whole paper dealt with loads rather than stresses, and there is
no evidence that in this connection the results have been misused (O'Connor
and Chan 1988a).
However, the writer simply cannot accept the final conclusion reached
in the discussion: "Bridge designers should not be alarmed by the very high
values of / reported by the authors; they are the result of misinterpretation
of the test data." The distinctive character of these results is that they are
for service vehicles; most other work on impact has been done with pre-
chosen test vehicles, and the chances that these are high-impact vehicles
are small. In this writer's opinion, conclusion 10 of the paper is still correct.
Although elastic impact values for a single girder may differ from those
for the bridge as a whole, it is simply not good enough for the authors to
argue as they have done from Fig. 18, for the provenance of this diagram
is unknown. For girder values of / for Six Mile Creek Bridge, it would be
necessary to analyze that bridge, with its heavy transverse diaphragm at
midspan, as shown in Fig. 1. Fig. 18 is for another case.
To obtain girder values of /, the procedure implicit in this paper would
1. Select the first mode corresponding to the maximum stress variation in
the selected girder.
2. Apply the dynamic vehicle, with its transverse location chosen to maximize
the effect on the chosen girder.
3. Compute values of /.
Prof., Dept. of Civ. Engrg., Univ. of Queensland, St. Lucia, Queensland 4067,
J. Struct. Eng. 1992.118:1708-1709.
The authors' comment on accuracy is also incorrect. As recorded in Table
1, O'Connor and Pritchard (1985) carried out two earlier series of tests for
/, in December 1981 and September 1983. The second of these tests was
carried out simply because the writer was surprised by the results of the
first. The bridge was then also calibrated with static loads. The quality of
the response was good. In this study, the performance of the bridge was
less reliable, possibly because of some intervening overload. However, the
values of / are entirely compatible with those of the proceeding study.
In closing, the authors quite correctly draw attention to values of / as
they affect elastic girder bending moments, and these were not given par-
ticular attention in this paper. Rather, the thrust of the paper was to use
field data to calibrate the dynamic vehicle model, recognizing that this could
then be used for a variety of cases, incuding the authors' case and many
There are also other important matters that should be addressed, such
as those raised in the last two conclusions of the paper. The use of prob-
abilistic design codes raises major difficulties in dealing with field data. The
occurrence of adjacent or following vehicles is being studied at the University
of Queensland, St. Lucia, Queensland, Australia, by R. J. Heywood with
the writer. A study has also been completed here on incremental collapse,
by Duczmal and Swannell, and it is hoped that this work will be published
shortly. There are other matters of at least equal importance, as in conclu-
sions 12 and 13. It is better to think in terms of causes and loads, rather
than in the direct application of values of /.
WIND PRESSURES ON BUILDINGS WITH MULLIONS3
Discussion by Charles D. Clift,3
Use of the word mullion by the curtain-wall industry sharply differs from
the connotation implied by the authors. Since a very significant amount of
exterior cladding in building construction involves curtain-wall and related
systems, consistent terminology or definitions should be acknowledged and
ASTM E 631 defines mullion as "a member used between windows or
doors as a means of connection, which may or may not be structural"
("Terminology" 1989). The American Architectural Manufacturers Asso-
ciation, which publishes many curtain-wall industry guides, defines mullion
as "a vertical or horizontal framing member separating fixed lights of glass"
Even with architects' penchant for postmodern designs, the great majority
of curtain wall mullions project no more than 6 or 8 in. (150 or 200 mm)
from the cladding surface. To call a cladding element that is 1 m or 2 m
deep a mullion is inappropriate and misleading.
"August, 1990, Vol. 116, No. 8, by Theodore Stathopoulos and Xiwu Zhu (Paper
Prin., Curtain Wall Design & Consulting, Inc., 10450 Brickwood Road, Dallas,
J. Struct. Eng. 1992.118:1708-1709.