Technical Papers
Sep 29, 2023

Determining Anchor Span Strand Tensions in the Completed State of a Suspension Bridge: An Analytical Algorithm

Publication: Journal of Bridge Engineering
Volume 28, Issue 12

Abstract

Integral components of suspension bridges are anchor spans, consisting of separate strands splayed from the main cable between the splay saddle and the front anchor plane. The main cable is separated into several strands and anchored to the anchorage through the twisting and dispersion of the splay saddle. Tensions in the anchor span strands are related to the overall structural safety of the suspension bridge, the geometric form, and internal stresses in the main cables generated in the completed bridge state. Therefore, the calculation and analysis of anchor span tension are particularly significant. Meanwhile, analyzing tensions in the anchor span strands is quite problematic, insofar as each strand in the saddle groove of the splay saddle is horizontally and vertically bent and then into a spatial catenary, while individual strands form a complex spatial system. This study first determines the spatial orientation of the anchor span strands passing over the splay saddle and their positions relative to the splay saddles. Analytical solutions are found by assuming that the strand tensions are equal at the point of tangency in each strand in the completed bridge state. Therefore, it can be ensured that the tensions in the anchor span strands are equal, which further leads to a sufficiently high safety factor for the cable strands. Given that the strands are separated from each other, an analytical approach is adopted for geometric coordination and mechanical analysis. Tensions in all anchor span strands, tangent position, and angle of each strand in the splay saddle can be determined quickly and precisely. A regular distribution pattern about the calculation results is observed according to the relative position of strands. A comparative validation is performed for strand tensions calculated theoretically against the measured values in a calculation example, proving the feasibility and high accuracy of the proposed method.

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Data Availability Statement

All data, models, and codes generated or used during the study appear in the published article.

Acknowledgments

The work described in this paper was financially supported by the National Key R&D Program of China (No. 2022YFB3706703), the National Natural Science Foundation of China (Grant No. 52078134), and the Research and Development Project of China Communications Construction (No. YSZX-02-2021-01-B), which are gratefully acknowledged.

Notation

The following symbols are used in this paper:
A
anchor point of the strand in the anchorage;
ai
parameter of the catenary equation;
bi
parameter of the catenary equation;
C1
center of the first vertical bend arc of the splay saddle;
C2
center of the horizontal bend arc of the splay saddle;
ci
parameter of the catenary equation = −Hai/q;
e1,i
moment arm of the horizontal component of strand tension at Q with respect to J;
e2,i
moment arm of the vertical component of strand tension at Q with respect to J;
e3
moment arm of the horizontal component of main cable tension in the side span at S with respect to J;
e4
moment arm of the vertical component of main cable tension in the side span at S with respect to J;
e5
moment arm of the gravity of the splay saddle with respect to J;
G
gravity of the splay saddle;
H
horizontal component of main cable tension in the side span;
Hai
horizontal component of the tension of the ith strand;
IP
intersection point of the catenary extension line of side span and anchor span;
J
rotation center of the splay saddle;
lai
projected length between Points A and Q onto the x-axis of the ith strand;
Mai
bending moment exerted by the tension in each strand on the splay saddle;
Ms
bending moment exerted by the main cable tension in the side span on the splay saddle;
MP
bending moment resulting from the gravity of the splay saddle;
P
point of tangency to the horizontal bend of the strands;
Q
point of tangency to the vertical bend of the strands;
q
dead weight of the strand per linear meter;
R1
distance from Point IP to Point C1;
R2
distance from Point IP to Point J;
R3
distance from the center of gravity of the splay saddle to Point J;
r1
radius of the first vertical bend arc of the splay saddle;
r2
radius of the second vertical bend arc of the splay saddle;
r3
radius of the third vertical bend arc of the splay saddle;
r4
radius of the fourth vertical bend arc of the splay saddle;
r5
radius of the horizontal bend arc of the splay saddle;
S
point of tangency of the main cable close to the side span;
Ti
tension of the ith strand in the anchor span;
U
starting point of the horizontal bend of the strands;
XC1
longitudinal coordinate of Point C1 in the global coordinate system;
XJ
longitudinal coordinate of Point J in the global coordinate system;
xPi
longitudinal coordinate of Point P in the plane coordinate system of the ellipse;
YC2
transverse coordinate of Point C2 in the global coordinate system;
YJ
transverse coordinate of Point J in the global coordinate system;
yPi
transverse coordinate of Point P in the plane coordinate system of the ellipse;
ZC1
vertical coordinate of C1 in the global coordinate system;
ZJ
vertical coordinate of J in the global coordinate system;
α
tangential angle of the main cable close to the side span;
βi
tangential angle to the vertical bend at Q of the ith strand;
βi
tangential angle to the vertical bend at P of the ith strand;
γi
tangential angle to the horizontal bend of the ith strand;
ΔXa,1
longitudinal distance between the center of the first arc segment and the center of the second arc segment of the splay saddle;
ΔXa,2
longitudinal distance between the center of the second arc segment and the center of the third arc segment of the splay saddle;
ΔXa,3
longitudinal distance between the center of the third arc segment and the center of the fourth arc segment of the splay saddle;
ΔXai,4
longitudinal distance between the center of the fourth arc segment of the splay saddle and Point P;
ΔXai,4
longitudinal distance between the center of the fourth arc segment of the splay saddle and Point Q;
ΔXAJi
distance in the longitudinal direction between Points A and J of the ith strand;
ΔXC2J
distance in the longitudinal direction between Points C2 and J;
ΔXPJi
distance in the longitudinal direction between Points P and J of the ith strand;
ΔXQPi
distance in the longitudinal direction between Points Q and P of the ith strand;
ΔYAJi
distance in the transverse direction between Points A and J of the ith strand;
Δyi
distance in the transverse direction between Points A and Q of the ith strand;
ΔYPJi
distance in the transverse direction between Points P and J of the ith strand;
ΔYQPi
distance in the transverse direction between Points Q and P of the ith strand;
ΔZa,1
elevation difference between the center of the first arc segment and the center of the second arc segment of the splay saddle;
ΔZa,2
elevation difference between the center of the second arc segment and the center of the third arc segment of the splay saddle;
ΔZa,3
elevation difference between the center of the third arc segment and the center of the fourth arc segment of the splay saddle;
ΔZai,4
elevation difference between the center of the fourth arc segment of the splay saddle and Point P;
ΔZai,4
elevation difference between the center of the fourth arc segment of the splay saddle and Point Q;
ΔZAJi
elevation difference between Points A and J of the ith strand;
Δzi
elevation difference between Points A and Q of the ith strand;
ΔZPJi
elevation difference between Points P and J of the ith strand;
ΔZQPi
elevation difference between Points Q and P of the ith strand;
η
inclination angle of the splay saddle;
θ0
included angle between the radius of the first arc segment of the splay saddle (close to the side span) and the vertical line;
θ1
central angle of the first vertical bend arc of the splay saddle;
θ2
central angle of the second vertical bend arc of the splay saddle;
θ3
central angle of the third vertical bend arc of the splay saddle;
θ4
central angle of the fourth vertical bend arc of the splay saddle;
φ1
included angle between the line connecting Points IP and C1 and the vertical line;
φ2
included angle between the line connecting Points IP and J and the vertical line; and
φ3
included angle between the line connecting the center of gravity and Point J and the vertical line.

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Go to Journal of Bridge Engineering
Journal of Bridge Engineering
Volume 28Issue 12December 2023

History

Received: Mar 11, 2023
Accepted: Aug 16, 2023
Published online: Sep 29, 2023
Published in print: Dec 1, 2023
Discussion open until: Feb 29, 2024

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Authors

Affiliations

Professor, Key Laboratory of Concrete and Prestressed Concrete Structures of the Ministry of Education, Southeast Univ., Nanjing 211189, China (corresponding author). ORCID: https://orcid.org/0000-0002-8272-1121. Email: [email protected]
Xiao-yi Zhang [email protected]
Master’s Candidate, Key Laboratory of Concrete and Prestressed Concrete Structures of the Ministry of Education, Southeast Univ., Nanjing 211189, China. Email: [email protected]
Gen-min Tian [email protected]
Ph.D. Candidate, Key Laboratory of Concrete and Prestressed Concrete Structures of the Ministry of Education, Southeast Univ., Nanjing 211189, China. Email: [email protected]

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